Nanocomposite for combustion application

ABSTRACT

The present invention generally concerns isolated nanoparticles via the decomposition of a ternary metal hydride. More specifically, the present invention harnesses increased energy densities from two distinct nanoparticles isolated by a precise decomposition of LiAlH4. The singular material is air stable and is a nanocomposite of Li3AlH6 nanoparticles, elemental Al nanoparticles, an amount of Ti metal, and a nanoscale organic layer, which we call nMx. The nanocomposite protects and preserves the high energy densities of the core metals isolated from the controlled reaction and makes the nanoparticles safe to handle in air. The final composite is devoid of byproducts or phase transitions that will decrease the energy output of the nanocomposite. The method of the present invention creates a narrow distribution of nanoparticles that have unique burning characteristics useful for many applications.

RELATED APPLICATIONS

This patent application claims priority to and is a divisional patentapplication of U.S. patent application Ser. No. 15/659,557 filed on Jul.25, 2017, which is pending. U.S. patent application Ser. No. 15/659,557claims priority to and is a continuation-in-part of U.S. patentapplication Ser. No. 14/259,859 filed on Apr. 23, 2014, which is nowabandoned. U.S. patent application Ser. No. 15/659,557 claims priorityto U.S. Prov. Pat. App. No. 62/377,562 filed on Aug. 20, 2016. U.S.patent application Ser. No. 15/659,557 claims priority to U.S. Prov.Pat. App. No. 62/380,367 filed on Aug. 27, 2016. U.S. patent applicationSer. No. 15/659,557 claims priority to U.S. Prov. Pat. App. No.62/517,194 filed on Jun. 9, 2017. U.S. patent application Ser. No.15/659,557 also claims priority to PCT/US2016/046760 filed on Aug. 12,2016, where PCT/US2016/046760 claims priority to U.S. Prov. Pat. App.No. 62/205,448, filed Aug. 14, 2015.

GOVERNMENT INTEREST

This invention was made with government support under SubrecipientAgreement No. RSC10011, Rev. No. 1; Prime Cooperative Agreement No.FA8650-10-2-2934 awarded by US Air Force Research Lab NanoenergeticsProgram and CHE-0963363 awarded by the National Science Foundation. TheGovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention generally concerns isolated nanoparticles via thedecomposition of a ternary metal hydride. More specifically, the presentinvention harnesses increased energy densities from two distinctnanoparticles isolated by a precise decomposition of LiAlH₄. Thesingular material is air stable and is a nanocomposite of Li₃AlH₆nanoparticles, elemental Al nanoparticles, an amount of Ti metal, and ananoscale organic layer. We call this nanocomposite nMx. Thenanocomposite protects and preserves the high energy densities of thecore metals isolated from the controlled reaction and makes thenanoparticles safe to handle in air. nMx is devoid of byproducts orphase transitions that will decrease the energy output of thenanocomposite. The method of the present invention creates a narrowdistribution of nanoparticles that have unique burning characteristicsuseful for many applications.

BACKGROUND OF THE INVENTION

Of Combustion & Work

Combustion and fire represent the earliest reactions used to performwork. It involves the burning of a fuel in the presence of an oxidizerto produce heat, potential flames and smoke, and reaction byproducts(gases). All chemical changes due to combustion are accompanied by theflow of heat energy into or out of a chemical system. Processes that canperform work take advantage of energy flow from fuels during oxidationreactions.

Industry is constantly seeking new source materials, or advanced fuels,that produce a great amount of heat at a reasonable cost. The presentinvention meets this need by disclosing a nanomaterial that displaysunique combustion characteristics. nMx is a nanocomposite of Li₃AlH₆nanoparticles, elemental Al metal nanoparticles, an amount of Ti metal,and a nanoscale organic layer. The present invention's heat ofcombustion, ΔH°, is higher than historical ΔH° values for burningmaterials typically used as advanced fuels.

Having high energy densities is an important measure for novel fuels andenergetic materials. Higher energy densities indicate that a materialcan do more work while having a lighter mass and/or volume, which is ofparticularly importance as it impacts the ability to launch payloadsinto space, lightens the weight of aircrafts to fly faster, and givesthe creation of munitions more flexibility.

Our composite falls within many classifications of advanced fuels due toits air-stability and tune-able combustion properties. We tune thechemical composition of our nanocomposite to ensure an energy density(both volumetric and gravimetric) that is suited for use as an additiveto liquid propellants, a solid propellant, as additives to high energymaterials, for use with explosives, pyrotechnics, for use as a sourcematerial for welding reactions, and as a source material for advancedmaterials production.

Metal Particles & Combustion

Due to the present invention disclosing the combustion of two distinctnanosized core metals, we address the importance of metals that burn.The combustion characteristics of metal particles make them viablealternatives to high energy fossil fuels. Iron or aluminum can bemilled, or synthesized, and turned into solid fuel grains for liftingpayloads into space or creating thermite hot enough to cut throughsteel. Some metal powders burn like hydrocarbon fuels. The energy andpower of a metal-burning engine are comparable to traditional combustionengines. Metal powders often have shorter ignition delays, they burnfaster, and have a higher volumetric energy density (energy per unitvolume of fuel) than do fossil fuels and other organic materials. Anincreased volumetric energy density reduces the size of the launchvehicle and improves efficiency through better aerodynamics.

Creating metal particles with high-energy output is challenging. Thereare serious safety concerns in handling the starting materials andreactant products, unfeasible reaction times, high production costs, andcompeting reactions at the metal's surfaces. The present inventiondiscloses nMx as a nanocomposite that overcomes such hurdles andproduces novel burning profiles by harnessing the combustion propertiesof a homogeneous mixture of Li₃AlH₆ nanoparticles, elemental Alnanoparticles, an amount of Ti metal, and a nanoscale organic layer. Theenergetic nanoparticles are safe to handle in air for use inapplications.

Aluminum Metal & Combustion

Aluminum is a valuable and versatile metal. Small aluminum particles arecommonly used as an additive to propellants to increase energy output ofa material or base fuel, a non-limiting example being nanoscale aluminumincreasing the ignition probability of diesel fuels [1]. Almicro-particles are used in kiloton amounts for solid rocket boostersand other solid rocket propellants. While there are many applicationsfor nanoscale aluminum materials, there are challenges with producingair stable aluminum nanoparticles having diameters smaller than 100 nmfor industrial or commercial use.

When not in its neutral elemental (0) oxidation state, natural aluminumexists in a ⁺3-oxidation state. Any process to reduce Al³⁺ to Al⁰, bygaining the three electrons, requires a large amount of energy. Becauseof its high reactivity, pure aluminum readily reacts with oxygen orwater to form a layer of aluminum oxide or hydroxide on its outersurfaces, which explains why pure aluminum is mostly found and used inone of its many oxidized forms, non-limiting examples being Al₂O₃ or themineral bauxite.

The oxide layer that forms on aluminum's surfaces greatly reduce themetal's combustion properties. The oxide blocks the core metal. Thisblocking slows the combustion process, and it prevents systems needing ahigh-energy output and a high burn rate from taking full advantage ofthe metal's ability to combust.

In smaller nanoparticles, aluminum's oxide layer can account for morethan 70% of the nanoparticle's mass. The combustion inefficiency ofaluminum metal increases for nanoparticles with diameters less than 20nm. The oxide coating significantly lowers the nanoparticle's energydensity, slows the nanoparticle combustion rate, may prevent completealuminum nanoparticle consumption, and can reduce hydrogen absorptionfor storage applications.

Commercially available aluminum is very inefficient as a fuel or fueladditive. A non-limiting example being solid fuels using ammoniumperchlorate, NH₄ClO₄, as an oxidizer for reducing aluminum metal beadsbound to solid rubber. Once the rubber is ignited and starts to burn,the oxidizer reacts exothermically with the fuel, thereby forming O²⁻and Al³⁺ and producing an energy release. Oxygen diffuses into the outerlayer of the metal to form aluminum oxide, Al₂O₃. The oxygen from theoxidizer can only diffuse by about 20 microns into the surface of apre-coated aluminum bead. Every single aluminum bead has a coating ofAl₂O₃ that is approximately 100 nm thick. A fair amount of the aluminummetal does not participate in combustion due to the protective oxidizedlayer on each bead.

This phenomenon is evidenced by the expulsion of byproducts duringrocket launches. Molten aluminum chunks are ejected from the nozzle as anon-contributory element to gas expansion and thrust. When aluminumbeads burn, the Al₂O₃ coating thickens. The additional oxide furtherslows combustion by reducing the amount of pure aluminum metal thatparticipates in reduction to create an effective energy release for acombustion engine. The passivated surfaces of the present invention givea greater amount of surface reactivity for both Li₃AlH₆ nanoparticlesand elemental Al nanoparticles for combustion events.

Recounting Li₃AlH₆

The production of complex metal hydrides has a somewhat convolutedpurpose, where some seek reducing agents, others seek a hydrogen storagematerial, and still others seek ways of exploiting the material as anadvanced fuel or additive. The purpose often dictates the method ofmaking these materials, e.g. ball milling, using varied startingmaterials for solvent based synthesis, and the like, thereby producingdispersions and a range of sizes within a bulk metal.

Although lithium aluminum hexahydride, Li₃AlH₆, sparks the imaginationas an energy source, it is a difficult material to work with. There aremany drawbacks to Li₃AlH₆ being a viable energy source. Li₃AlH₆ iswildly expensive, where the pricing for 1 kg of Li₃AlH₆ can run as highas $20,000 USD. Li₃AlH₆ is unstable and reacts with water and ambientgases to produce spontaneous burning. In their “natural” form most metalhydrides are not safe to handle in air. Because our nanocomposite is afirst reporting of a cost-effective method for creating stabilizedLi₃AlH₆ nanoparticles, making Li₃AlH₆ nanoparticles air safe andsensible for applications, we present a brief retelling of importantmoments for Li₃AlH₆.

Synthesis of Li₃AlH₆ was first reported by Ehrlich et al. in the late1960's, and the thermal decomposition of LiAlH₄ into Li₃AlH₆ was laterreported by Dilts and Ashby in the early 1970's. Since then, LiAlH₄ hasbecome commonly used in industrial processes as a reducing agent toconvert esters, carboxylic acids, acyl chlorides, aldehydes, andkeytones into their corresponding alcohols, as drying agents, and asmaterials for hydrogen gas storage [2-4].

LiAlH₄ and Li₃AlH₆, as with most of the metal hydrides, are highlyreactive with water and ambient gases. These chemicals are pyrophoricand must be carefully handled and stored. When LiAlH₄ is heated, Diltsand Ashby found that the thermal decomposition of LiAlH₄ occurs in threesteps as follows:3LiAlH₄→Li₃AlH₆+2Al+3H₂(150° C.-170° C.),  (R1)2Li₃AlH₆→6LiH+2Al+3H₂(185° C.-200° C.),  (R2)LiH+Al→LiAl+½H₂(above 400° C.).  (R3)

LiAlH₄ is metastable at room temperature and partially decomposes intoLi₃AlH₆ over very long periods of time. However, reaction steps R2 andR3 will occur at temperatures above 150° C. Meaning, to make nMx, it isvital to hold the reaction vessel below 150° C. to keep thedecomposition of LiAlH₄ to R1, where we further alter the surfaces ofLi₃AlH₆ nanoparticles and elemental Al nanoparticles as needed [4].

In 1963, the heat of formation for Li₃AlH₆ was measured as ΔH₂₉₈°=−79.40kcal/mol. The reaction was driven in 4 N HCl in a closed bomb, where thefinal ΔH₂₉₈° value was estimated from ΔH₂₉₈° values obtained foraluminum, lithium, and Li₃AlH₆ [5]. Zaluska et al. reports a DSC scanfor ball milled bulk Li₃AlH₆ having a burn event at about 240° C.-260°C. [20].

Chen et al. uses a vibrating mill technique to make nanocrystallites ofLiAlH₄ and Li₃AlH₆, where two different experiments are performed tomeasure H₂ gas desorption and resorption [6]. Firstly, Chen et al.vibrate mills LiAlH₄ along with titanium chloride anhydrous aluminumreduced (TiCl₃.⅓AlCl₃) for up to one hour. They report that alkoxidecatalysts, such as titanium-n-butoxide (Ti(OBu)₄), are highlyproblematic for their reversible hydrogen experiments. Chen et al. millsLiAlH₄ into a micro scaled (μm) powder that contains a range of particlesizes, including dispersed LiAlH₄ nanocrystals below 20 nm. However,Chen et al. could not convert LiAlH₄ into both Li₃AlH₆ nanoparticles andelemental Al nanoparticles [6].

Secondly, in a separate experiment, Chen et al. vibrate mills2LiH+LiAlH₄ along with titanium chloride anhydrous aluminum reduced(TiCl₃.⅓AlCl₃) for up to one hour to create Li₃AlH₆. The result is TiCl₃doped Li₃AlH₆ nanocrystals that are granular shaped at about 20 nm. Chenet al. believe the Li₃AlH₆ nanocrystals are due to many factorsincluding the presence of a separate Ti phase and a nanocrystalline Aland Ti_(x)Al_(y) phase associated with the milled powder [6]. However,Chen et al. does not give PXRD data substantiating the presence of Alnanocrystals in their powder, which should give strong PXRD peaks interms of 2Θ at ˜37°, ˜45°, ˜65°, and ˜78° as compared to other methodsthat report PXRD peaks for elemental Al nanoparticles [7].

In both instances, Chen et al. does not create a true nanoparticlesystem by stopping the decomposition of LiAlH₄ at the first reactionstep. Chen et al. examines the catalytic effect of a Ti⁰/Ti²⁺/Ti³⁺defect on H₂ formation and resorption of Li₃AlH₆. Chen et al. continuesthe reaction through Li₃AlH₆ decomposition, 2Li₃AlH₆→6LiH+2Al+3H₂. Theycreate large bundles of multiple nanocrystals that have been fusedtogether by cold welding, where the creation and extraction of singlecrystal nanoparticles is impossible. Also note that Chen et al.'snanocrystalline domains are randomly dispersed within a system that isprimarily bulk material that range from about 1 μm to about 10 μm insize [6].

U.S. Pat. Pub. No. 2003/0026757 as filed by Percharsky et al. disclosesthe release of hydrogen gas from mechanical processing of a metalhydride at room temperature. In one instance, the starting material maybe LiAlH₄. The reaction takes place in the absence of any solvents toforcefully collect hydrogen gas from the storage material. The processdoes not use any nanostructures [8].

Choi et al. disclose the use of a Li₃AlH₆/LiBH₄ mixture as a reversiblestorage medium for making hydrogen gas via ball milling. Choi et al.'sball milling conditions are adjusted to account for unexpected reactionsor changes in the original phases [9]. The process of ball millingresults in aggregated nanocrystallites that morph into larger mesoscalestructures that are not nanoparticles. All materials were unstable inair and were handled in a glove box under an inert atmosphere.

Varin et al. disclose the effects of ball milling on nm sized (300 nm to90 nm±30 nm) LiAlH₄. Through DSC data, they report a thermaldecomposition of LiAlH₄ to micron sized Li₃AlH₆ between 190° C.-300° C.[24]. Varin et al. does not create a true nanoparticle system bystopping the decomposition of LiAlH₄ at the first reaction step. Varinet al. continues the reaction past Li₃AlH₆ decomposition to form LiH andAl molecules, 2Li₃AlH₆→6LiH+2Al+3H₂ [24].

U.S. Pat. Pub. No. 2011/0165061 as filed by Yang et al. discloses amethod of increasing thermal conductivity in hydrogen storage systems[10]. Yang creates a reversible reaction for making hydrogen gas byforcing Li₃AlH₆ and Mg(NH₂)₂ to liberate hydrogen under certain thermalconditions. Because metal hydrides are inherently poor thermalconductors, Yang et al. cool their ball milled particles with analuminum film that acts as a heat sink. All of Yang et al.'s materialsare air unstable.

The present invention is the first to harness the energetic propertiesof nanoscaled products created from the thermal decomposition of LiAlH₄for combustion processes. None of the references disclose a bottom-upsynthesis that creates a homogenous material composed of nanoparticlesof both Li₃AlH₆ and elemental Al metal that are carefully sized andpassivated by a nanoscale organic layer at the first reaction step ofLiAlH₄ decomposition. nMx is air stabilized, contains a certain amountof Ti metal, is safe to handle, and protects and preserves thecombustion properties of the same for energy applications. Therefore,there is a need for the present invention.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide a nanocomposite forcombustion applications being a homogenous mixture of two distinct coremetals including a first nanoparticle that is a metal hydride and asecond nanoparticle that is an elemental post-transitional metal. Thesurfaces of both nanoparticles are associated with an amount of titaniummetal, and both are air stabilized by a nanoscale organic layer being afatty acid, a fatty alcohol, an alkadiene, or any mixture or combinationthereof.

It is an aspect of the present invention where the first nanoparticle isLi₃AlH₆ and the second nanoparticle is elemental Aluminum metal, whereinboth are associated with an amount of Ti metal and are passivated andair stabilized by a nanoscale organic layer.

It is an aspect of the present invention where the nanoscale organiclayer is a fatty acid, a fatty alcohol, an alkadiene, or any mixture orcombination thereof, wherein the nanoscale organic layer passivates andair stabilizes the surfaces of both the Li₃AlH₆ nanoparticle and theelemental Al nanoparticle and includes: 1,7-octadiene, 1,9-decadiene,myrcene, or 1,13-tetradecadiene, 1,3-butadiene, isoprene,2-methyl-1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene,2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-pentadiene,1,3-hexadiene, 2-methyl-1,3-hexadiene, 1,3-heptadiene,3-methyl-1,3-heptadiene, 1,3-octadiene, 3-butyl-1,3-octadiene,3,4-dimethyl-1,3-hexadiene, 3-n-propyl-1,3-pentadiene,4,5-diethyl-1,3-octadiene, 2,4-diethyl-1,3-butadiene,2,3-di-n-propyl-1,3-butadiene, and 2-methyl-3-isopropyl-1,3-butadiene,fatty alcohols being tert-butyl alcohol, tert-amyl alcohol,3-methyl-3-pentanol, ethchlorvynol, 1-octanol (capryl alcohol),pelargonic alcohol (1-nonanol), 1-decanol (decyl alcohol, capricalcohol), undecyl alcohol (1-undecanol, undecanol, hendecanol), laurylalcohol (dodecanol, 1-dodecanol), tridecyl alcohol (1-tridecanol,tridecanol, isotridecanol), myristyl alcohol (1-tetradecanol),pentadecyl alcohol (1-pentadecanol, pentadecanol), cetyl alcohol(1-hexadecanol), palmitoleyl alcohol (cis-9-hexadecen-1-ol), heptadecylalcohol (1-n-heptadecanol, heptadecanol), stearyl alcohol(1-octadecanol), nonadecyl alcohol (1-nonadecanol), arachidyl alcohol(1-eicosanol), heneicosyl alcohol (1-heneicosanol), behenyl alcohol(1-docosanol), erucyl alcohol (cis-13-docosen-1-ol), lignoceryl alcohol(1-tetracosanol), ceryl alcohol (1-hexacosanol), 1-heptacosanol,montanyl alcohol, cluytyl alcohol, or 1-octacosanol, 1-nonacosanol,myricyl alcohol, melissyl alcohol, or 1-triacontanol, 1-dotriacontanol(lacceryl alcohol), geddyl alcohol (1-tetratriacontanol), cetearylalcohol, carboxylic (fatty) acids being butyric acid [CH3(CH2)2COOH],valeric acid [CH₃(CH₂)₃COOH], caproic acid [CH₃(CH₂)₄COOH], enanthicacid [CH₃(CH₂)₅COOH], caprylic acid [CH₃(CH₂)₆COOH], pelargonic acid[CH₃(CH₂)₇COOH], capric acid [CH₃(CH₂)₈COOH], undecylic acid[CH₃(CH₂)₉COOH], lauric acid [CH₃(CH₂)₁₀COOH], tridecylic acid[CH₃(CH₂)₁₁COOH], myristic acid [CH₃(CH2)₁₂COOH], pentadecylic acid[CH₃(CH₂)₁₃COOH], palmitic acid [CH₃(CH₂)₁₄COOH], margaric acid[CH₃(CH₂)₁₅COOH], stearic acid [CH₃(CH₂)₁₆COOH], nonadecylic acid[CH₃(CH₂)₁₇COOH], arachidic acid [CH₃(CH₂)₁₈COOH], or any combinationthereof.

It is an aspect of the present invention wherein the abovenanocomposites have a measured energy density from −38 kJ/g to −35 kJ/g.

It is an aspect of the present invention wherein the nanoscale organiclayer also includes glycols, of various molecular weights, being PEG,PEO, tetraethylene glycol, triethylene glycol, or any combinationthereof in mixture with a fatty acid, a fatty alcohol, or an alkadiene.

It is an aspect of the current invention wherein the nanocomposite has ananoscale organic layer that is a combination of octadecanol andtetraethylene glycol in a respective ratio mixture of 23% to 77% or 70%to 30% and has an energy density of −29 kJ/g.

It is an aspect of the current invention wherein the nanocomposite has ananoscale organic layer that is a combination of steric acid andtetraethylene glycol in a respective ratio mixture of 23% to 77% or 70%to 30% and has an energy density of −29 kJ/g.

It is an aspect of the present invention for the nanocomposite to havean amount of Ti metal associated with the Li₃AlH₆ nanoparticles and theelemental Al nanoparticles. The amount of Ti metal is from 0.05% to 1.0%of the total weight of the nanocomposite.

It is yet another aspect of the present invention for the Li₃AlH₆nanoparticles to have a diameter from 15 nm to 100 nm and the elementalAl nanoparticles to have a diameter from 7 nm to 100 nm.

It is an embodiment of the present invention for the amount of Ti metalto originate from a titanium(IV) compound, a titanium(IV) alkoxide, atitanium(IV) tetraalkoxylate, titanium(IV) isopropoxide (Ti(O^(i)Pr₄,97%), or a titanium(IV) tetraaryloxylate.

It is yet another aspect of the present invention for the nanoscaleorganic layer about the surfaces of both core metal nanoparticles to befractionally tuned from 25% to 75% by weight to modify the burn ratecharacteristics of the nanocomposite.

It is an aspect of the present invention for the nanocomposite toexhibit a combustion event for the Li₃AlH₆ nanoparticles between 180° C.and 210° C., a combustion event for the nanoscale organic layer between275° C. and 325° C., and a combustion event for the elemental Alnanoparticles between 575° C. and 610° C.

It is yet another aspect of the present invention wherein thenanocomposite is characterized by PXRD peaks for both nanoparticles andthe Raman fundamental stretching frequencies of nanoscale organic layeras follows: Li₃AlH₆ nanoparticles giving a PXRD diffractogram havingdouble peaks for 2Θ at 21.9°, at 22.5°, and at 31.7°, elemental Alnanoparticles giving PXRD peaks at 2Θ at 38.4° [highest peak], 44.7°, at65.1°, at 78.2°, and 82.4°; and the nanoscale organic layer giving Ramandata for C—O stretching frequencies from 1092 cm⁻¹ to 1294 cm⁻¹, C═Ostretching frequencies of 1645 cm⁻¹, and C—H stretching frequencies from2839 cm⁻¹ to 3024 cm⁻¹.

It is an embodiment of the present invention wherein the nanoscaleorganic layer is a monomer that can undergo polymerization,cross-linking, or copolymerization to form a matrix about both distinctnanoparticles.

It is an aspect of the present invention for the nanoscale organic layerfor both Li₃AlH₆ nanoparticles and elemental Al nanoparticles to impartair stability to the nanocomposite for safe handling in ambientconditions and wherein the nanoscale layer contains an oxygen atom massfrom 5% to 34%.

BRIEF DESCRIPTION OF THE FIGURES

The following figures are non-limiting examples of the present inventionand are not intended to narrow the scope of the same.

FIG. 1 depicts a bottom up synthesis for the nMx nanocomposite 9. Tialkoxides 2 react to decompose LiAlH₄ 1 at 100° C. The alkoxide 2 actsas a nanoparticle initiator, where the decomposition of LiAlH₄ 1 createsmolecular seeds of Li₃AlH₆ 3 a and elemental Al 3 b metals by which thenanoparticles grow. A passivation agent 4 is added to the reaction. Amonolayer passivation scheme 7 is detailed using hydrophobic cappingagents 4 with a reactive head group. The reaction is stopped when thepassivated nanoparticles 5, 6 are roughly from about 8.5 nm to 100 nm indiameter, where Ti 8 remnants associate with both the Li₃AlH₆nanoparticles and the elemental Al nanoparticles in the final nMxnanocomposite 9.

FIG. 2 depicts a bottom up synthesis for the nMx nanocomposite 14. Tialkoxides 2 react to decompose LiAlH₄ 1 at 100° C. The alkoxide 2 actsas a nanoparticle initiator, where the decomposition of LiAlH₄ 1 createsmolecular seeds of Li₃AlH₆ 3 a and elemental Al 3 b metals by which thenanoparticles grow. A passivation agent 10 is added to the reaction.Here, passivation occurs through polymerization of the passivation agent10 about the surfaces of the Li₃AlH₆ nanoparticles 3 a and elemental Alnanoparticles 3 b using hydrophobic capping agents 10 with apolymerizable head group. The reaction is stopped when the passivatednanoparticles 12, 13 are roughly from about 8.5 nm to 100 nm indiameter, where Ti 8 remnants associate with both the Li₃AlH₆nanoparticles and the elemental Al nanoparticles in the final nMxnanocomposite 14.

FIG. 3 depicts, in chart form, variations in the oxygen atom masspercentages for the nanoscale organic layer used between nMx₁₀ andnMx₂₀. The nMx nanocomposites between nMx₁₀ and nMx₂₀ has oxygen atom(O) mass percentages between 0% and 42% respectively. The x-axis of FIG.3 shows the variation in passivation agents. The y-axis of FIG. 3represents the total mass fraction of organic in the nanocomposite. Atone end, nMx₁₀ has a polymerized organic hydrocarbon cap, where the Oatom mass percentage is 0%, and, at the other end, nMx₂₀, havingpolyethylene oxide capping structure, has an O atom mass percentage of˜42%.

FIG. 4 depicts a PXRD diffraction pattern for nMx₁₁, having peaks aboutthe x-axis rendered in degrees relative to 20. For FIGS. 4-9, the y-axisis labeled as Relative Intensity from 0% to 100%. The highest peak(100%) is attributed to elemental Al NPs at 38.4° and Li₃AlH₆ givesdouble peaks throughout the diffraction pattern. All PXRD diffractogramsgive nearly identical information for the core crystallinenanoparticles.

FIG. 5 depicts a PXRD diffraction pattern for nMx₁₂, having peaks aboutthe x-axis rendered in degrees relative to 2Θ. The y-axis is labeled asRelative Intensity from 0% to 100%. The highest peak (100%) isattributed to elemental Al NPs at 38.4° and Li₃AlH₆ gives double peaksthroughout the diffraction pattern.

FIG. 6 depicts a PXRD diffraction pattern for nMx₁₃, having peaks aboutthe x-axis rendered in degrees relative to 2Θ. The y-axis is labeled asRelative Intensity from 0% to 100%. The highest peak (100%) isattributed to elemental Al NPs at 38.4° and Li₃AlH₆ gives double peaksthroughout the diffraction pattern.

FIG. 7 depicts a PXRD diffraction pattern for nMx₁₆, having peaks aboutthe x-axis rendered in degrees relative to 2Θ. The y-axis is labeled asRelative Intensity from 0% to 100%. The highest peak (100%) isattributed to elemental Al NPs at 38.4° and Li₃AlH₆ gives double peaksthroughout the diffraction pattern.

FIG. 8 depicts a PXRD diffraction pattern for nMx₁₉, having peaks aboutthe x-axis rendered in degrees relative to 2Θ. The y-axis is labeled asRelative Intensity from 0% to 100%. The highest peak (100%) isattributed to elemental Al NPs at 38.4° and Li₃AlH₆ gives double peaksthroughout the diffraction pattern.

FIG. 9 depicts a PXRD diffraction pattern for nMx₂₀, having peaks aboutthe x-axis rendered in degrees relative to 2Θ. The y-axis is labeled asRelative Intensity from 0% to 100%. The highest peak (100%) isattributed to elemental Al NPs at 38.4° and Li₃AlH₆ gives double peaksthroughout the diffraction pattern.

FIG. 10 depicts FTIR stretching frequencies of the nanoscale organiclayer for nMx₂₀. The nanoscale organic layer is a glycol and shows aband at 1080 cm⁻¹ (C—O stretching in the glycol) and at 2850-2970 cm⁻¹(C—H stretching in the glycol). This indicates that the there is anassociation with the glycol nanoscale organic layer and the two distinctcore nanoparticles.

FIG. 11 depicts Raman scattering for nMx₁₂, where octadecanol is thenanoscale organic layer. The Raman scan is performed from 500 cm⁻¹ to3500 cm⁻¹. Octadecanol gave Raman frequencies for nMx₁₂ at about 1092cm⁻¹ (C—O stretch) and at about 2850-2920 cm⁻¹ (C—H stretch).

FIG. 12 depicts Raman scattering for nMx₁₃, where octadecanoic acid isthe nanoscale organic layer. The Raman scan is performed from 500 cm⁻¹to 3500 cm⁻¹. Octadecanoic acid gave Raman frequencies for nMx₁₃ atabout 1294 cm⁻¹ (C—O stretch), at about 1645 cm⁻¹ (C═O stretch), and atabout 2841-3024 cm⁻¹ (C—H stretch).

FIG. 13 depicts Raman scattering for nMx₁₆, where a mixture ofoctadecanol and TEG is the nanoscale organic layer. The Raman scan isperformed from 500 cm⁻¹ to 3500 cm⁻¹. The mixture of octadecanol and TEGgave Raman frequencies for nMx₁₆ from about 2839 cm⁻¹ to about 2915 cm⁻¹(C—H stretch). Note that the C—O stretch is too weak and not observable.

FIG. 14 depicts Raman scattering for nMx₁₉, where PEG is the nanoscaleorganic layer. The Raman scan is performed from 500 cm⁻¹ to 3500 cm⁻¹.PEG gave Raman frequencies for nMx₁₉ at about 1086 cm⁻¹ (C—O stretch)and at about 2868-2950 cm⁻¹ (C—H stretch).

FIG. 15 displays DSC-TGA curves for nMx₁₀ and commercial Li₃AlH₆ underambient air flow. The nanoscale organic layer is 1, 7-octadiene.

FIG. 16 displays DSC-TGA curves for nMx₁₁ under ambient air flow with amixture of epoxydecene and alkadiene as the nanoscale organic layer,where the starting materials are mixed at a ratio of 10:1:2 ofLiAlH₄:epoxydecene:octadiene respectively.

FIG. 17 displays DSC-TGA curves for nMx₁₂ under ambient air flow with50% steryl-alcohol as the nanoscale organic layer.

FIG. 18 displays DSC-TGA curves for nMx₁₃ under ambient air flow with44% oleic acid as the nanoscale organic layer.

FIG. 19 displays DSC-TGA curves for nMx₁₆ under ambient air flow with amixture of octadecanol/TEG as the nanoscale organic layer.

FIG. 20 displays DSC-TGA curves for nMx₁₉ under ambient air flow withPEG 600 as the nanoscale organic layer.

FIG. 21 depicts two separate TEM images of nMx₁₀, where core metalnanosurfaces are passivated by octa-diene as the nanoscale organiclayer.

FIG. 22 depicts TEM imaging of nMx₁₂, where core metal surfaces arepassivated by 50% steryl alcohol as the nanoscale organic layer.

FIG. 23 depicts TEM imaging of nMx₁₃, where the surfaces of the corenanoparticles are passivated by 44% oleic acid as the nanoscale organiclayer.

FIG. 24 depicts TEM imaging nMx₁₆, where core metal nanosurfaces arepassivated by a mixture of octadecanol/TEG as the nanoscale organiclayer.

FIG. 25 depicts TEM imaging for nMx₁₉, where core metal nanosurfaces arepassivated by PEG 600 as the nanoscale organic layer.

FIG. 26 depicts TEM imaging for nMx₂₀, where core metal nanosurfaces arepassivated by TEG as the nanoscale organic layer.

FIG. 27a and FIG. 27b display a relative comparison of shockwavevelocities of secondary high explosive PETN with and without nMx₂₀.

GENERAL EMBODIMENT OF THE INVENTION

From this point forward, the following words disclose our nanocomposite,methods for creating them, and practical uses thereof. Our invention isa singular material having two distinct nanoparticles, an amount of Timetal, and an organic nanoscale layer, i.e., lithium aluminumhexahydride (Li₃AlH₆) and elemental aluminum nanoparticles with anamount of Ti metal having passivated surfaces that display uniqueburning characteristics. Our process ensures that the nanocomposite isair stable and is safe to handle in air for use in applications. Thepresent invention protects and preserves the enhanced combustionproperties of the metal nanoparticles isolated during the reaction. Ourreaction conditions are carefully designed to form passivatednanoparticles having a nanoscale organic layer. However, our words arenot a limitation on the scope of the present invention but are writtento detail certain embodiments thereof. After reading the detaileddescription, modifications will become apparent to those skilled in theart, and those modifications are intended to be covered by ourdisclosure.

Definitions

The terms “nanoparticle,” “NP(s),” or “nanomaterial” generally refer tovery small particles having all three dimensions from about 1 nm and toabout 100 nm. Nanoparticles have a greater number of surface atomsrelative to the same chemical species in bulk or microscale (μm) form.In contrast, for bulk materials larger than one micrometer, thepercentage of atoms at the surface is minuscule relative to the totalnumber of atoms within the material, which is why bulk materialsgenerally have uniform physical properties throughout regardless of itssize. Because the percentage of atoms at the surface of a nanomaterialare significantly higher than that of the bulk form, nanomaterialsdemonstrate chemical and physical properties that are not found in thebulk, even when that bulk material includes a dispersion ofnanocrystalline domains [11, 12].

Nanoparticles are so small that their physical properties are notconstant as a function of their size because the percentage of atoms atthe surface of a material becomes significant, where these unique sizedependent properties can be described using quantum physics. Fornanospheres, size-dependent properties are observed, such as surfaceplasmon resonance in some metal particles, or increased magnetism for ametal that is significantly diminished as the metal moves into its bulkform.

Our invention examines and provides for air stable nanoparticles thatexhibit unique burning characteristics synthesized via a controlledbottom up reaction. Due to the larger number of atoms at ournanoparticle surfaces, fundamentally new combustion and hydrogenevolution behaviors are observed when our material is kept at thenanoscale, while being air stable, i.e. the present invention stabilizesLi₃AlH₆ nanoparticles and elemental Al metal nanoparticles, which aremore combustible than their bulk metal counterparts.

The term “nMx” generally refers to a singular material, being ananocomposite of lithium aluminum hexahydride nanoparticles, Li₃AlH₆,elemental Al metal nanoparticles, an amount of Ti metal, and a nanoscaleorganic layer. nMx exists in various iterations according to thenanoscale organic layer used to passivate the surfaces of the coremetals. Passivation makes nMx air-stable and protects and preserves thecombustion properties of the singular material isolated from thedecomposition of LiAlH₄.

The term “singular material” generally refers to the nanocompositenature of nMx being a homogeneous mixture of two distinct nanoparticles,Li₃AlH₆ nanoparticles, elemental Al metal nanoparticles, and an amountof Ti metal. All aspects of both core metals are subjected to nanoscaleorganic passivation.

The term “passivation” generally refers to a process of covering ormodifying the outer surfaces of a core material, being nanoparticles, tokinetically stabilize otherwise reactive molecules, where thestabilization substantially slows the ability of the underlying corematerial to react with oxidative or solvolytic agents.

The terms “nanoscale organic layer,” “NSOL,” “capping agents,” or“passivation agents” generally refer to organic ligands or monomericmaterials capable of polymerization or polymeric materials that coverthe outer surfaces of two distinct core metals, being nanoparticles, tokinetically stabilize otherwise reactive molecules, where thestabilization substantially slows the ability of the underlying corematerial to react with oxidative or solvolytic agents.

The term “thermite” generally refers to a combustible material thatintramolecularly coexists with its oxidant and does not require anexternal oxygen supply to sustain the ensuing redox reaction, e.g. thematerial exhibits self-sustaining combustion in an inert environment.

The term “nanothermite” generally refers to a thermite material composedof nanoparticles.

The term “organic ether” generally refers to an oxygen-containinghydrocarbon comprised of connecting ether C—O—C bonds, i.e. an oxygenatom connected to alkyl or aryl groups.

The term “amu” generally refers to atomic mass unit, a unit of molecularmass measurement relative to a carbon-12 standard.

The term “polymerization” generally refers to a chemical process ofbonding together multiple repeating units of a monomer, or differingmolecules, to form a larger chain-like matrix, or network typestructure. The monomer molecules may be alike, or they may representtwo, three, or more different compounds. Combined monomers make aproduct that has certain unique physical properties such as elasticity,high tensile strength, or the ability to form fibers that differentiatepolymers from substances composed of smaller and simpler molecules;often, many thousands of monomer units are incorporated in a singlemolecule of a polymer. The formation of stable covalent chemical bondsbetween the monomers sets polymerization apart from other processes,such as crystallization, in which large numbers of molecules aggregateunder the influence of weak intermolecular forces.

The term “copolymerization” generally refers to the process of two ormore different monomers bonding together to polymerize.

The term “organic matrix” generally refers to a three-dimensionalinterwoven net of polymer molecules that encompass a core nanoparticlematerial, or the ability of non-polymeric materials being monolayersabout the surfaces of the nanoparticles to self-assemble.

The term “isolated nanoparticles” generally refers to metal containingcores that are not in direct contact such that they do not form micronscale metal aggregates.

The term “initiator” generally refers to a chemical that speeds up areaction and is consumed in the reaction. In the present invention Tialkoxide initiates the decomposition of LiAlH₄, is consumed, and becomespart of the final nanocomposite.

The term “pyrophoric” generally refers to the ability of truenanoparticles to spontaneously burn in air.

The term “air stable or “air stability” generally refers to ourobservation that the metal nanoparticles of nMx₁₂-nMx₂₀ neitherspontaneously ignite nor rapidly react within seconds with ambientoxygen in air, primarily from H₂O and O₂. nMx₁₂ through nMx₂₀ are allair stable when using proper preparation methods as disclosed herein.nMx₁₀ is unstable in air, where larger amounts have pyrophoric hot spotsthat spontaneously ignite. nMx₁₁ is not as pyrophoric as nMx₁₀, butlarger quantities have pyrophoric hot spots, also making the materialslightly air unstable.

The term “air sensitive” or “air sensitivity” generally refers to asimilar but different property than air stability of reactive materials.Air sensitivity is the tendency for an energetic material to slowlyreact in air (primarily with water and molecular oxygen) to lose energydensity. This loss of energy density may take place over the timescaleof fractions of an hour, days, weeks, or longer periods of time. The airsensitivity of nMx is at a minimum for nMx₁₂ and nMx₁₃.

The term “terminal O—H cleavage” generally refers to the severing of anoxygen-hydrogen bond in an alcohol or carboxylic acid with a hydroxylfunctionality at the end of a hydrocarbon chain.

The term “dispersed” generally refers to a nonuniformed distribution ofnanoparticles or nanocrystalline deposits within a micron sized bulkmaterial.

The term “alkadiene” generally refers to a group of unsaturatedhydrocarbons that have two carbon-carbon double bonds that can bepolymerized anionically (i.e., in a reaction initiated by anorgano-alkali metal), or via free radical polymerization, where thedouble bonds may be cumulated, isolated, or conjugated. An alkadiene mayhave the general formula of C_(n)H_(2n-2). Examples of conjugated dienehydrocarbons may include, but are not limited to, 1,7-octadiene,1,9-decadiene, myrcene, or 1,13-tetradecadiene, 1,3-butadiene, isoprene,2-methyl-1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene,2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-pentadiene,1,3-hexadiene, 2-methyl-1,3-hexadiene, 1,3-heptadiene,3-methyl-1,3-heptadiene, 1,3-octadiene, 3-butyl-1,3-octadiene,3,4-dimethyl-1,3-hexadiene, 3-n-propyl-1,3-pentadiene,4,5-diethyl-1,3-octadiene, 2,4-diethyl-1,3-butadiene,2,3-di-n-propyl-1,3-butadiene, and 2-methyl-3-isopropyl-1,3-butadiene,or combinations thereof.

The terms “energy,” “enthalpy,” and “heat” are generally usedinterchangeably herein, where the important quantitative measurement ofheat is via enthalpies. The amount of combustible energy, or heat,generated via a reaction is dictated by the chemical and energeticproperties of the source material. Energy, (E), for combustion reactionsmay be defined as:E=q+w,where (E) is the sum of heat (q) plus work (w). Heat and work aretypically path functions. Heat is the energy flow associated withchanges in temperature of the source material. Work may take many forms,but it is typically associated with the ability of the heat energy tobring about mechanical or physical changes to its surroundings.

The term “work,” as it relates to combustion processes, may be generallydefined by the equation:w=−PΔV,where P=pressure against the system it is working upon, and ΔV is thesystem volume change.

The term Enthalpy (H) generally refers to the equation:H=E+PV.Energy and enthalpy are state functions that give enthalpy as equal toheat at constant pressure (q_(p)):H=q _(p).Therefore, enthalpy is typically called “heat” and the “enthalpy ofcombustion” is called “heat of combustion,” where the heat ofcombustion, ΔH°, indicates the amount of heat energy created per mol ofa burning source material [kJ/mol]. The heat of combustion, or the heatof reaction, is defined by the following equation:ΔH° _(reaction) =ΣΔH° _(f)(products)−ΔH° _(f)(reactants),ΔH° reaction of a chemical reaction is the net difference for the amountof heat gained or lost between the products and reactants under constantpressure in relation to the amount of work being done by the reaction,given as ΔH°_(f)(products)−ΔH°_(f)(reactants). More importantly,enthalpy is the heat per unit amount of substance. It is most oftenexpressed as kJ/mol (molar heat), kJ/g (gravimetric energy density), orkJ/cm³ (volumetric energy density).

The term “thermoplastic” generally refers to thermoplastic polyurethane,styrene block-copolymers, thermoplastic silicone elastomer, aliphatic orsemi-aromatic polyamides, thermoplastic vulcanisate, acrylonitrilebutadiene styrene (ABS), polylactic acid, polyvinyl alcohol,polycarbonate, polymethylmethacrylate, polyethylene, polypropylene,polystyrene, nylon, polycarbonate, polyvinyl chloride, Teflon, or anycombination thereof.

The term “base material” generally refers to a feed stock for a 3Dprinter being a mixture of a thermoplastic polymer suitable for 3Dprinting, an amount of at least one nMx nanocomposite, and other fuelsor additives.

The term “Ti” generally refers to the chemical element titanium. It is atransition metal with atomic no. 22. In the current invention, it isassociated with the nanoparticles surfaces of Li₃AlH₆ and elemental Aland is generated from a titanium(IV) compound, a titanium(IV)tetraalkoxylate, titanium(IV) isopropoxide (Ti(O¹Pr₄, 97%), or atitanium(IV) tetraaryloxylate.

LiAlH₄ Decomposition Via a Bottom Up Reaction

The present invention harnesses the high energy densities of Li₃AlH₆nanoparticles and elemental Al nanoparticles by exploiting the thermalcatalytic decomposition of LiAlH₄. A bottom up reaction gives a finalcomposite that has a greater number of surface atoms resulting inincreased energy densities for each nanoparticle. The precise reactionmethod uses a catalyst to ensure that a significant number of bothnanoparticles are generated and the nanoscale organic layer successfullyair stabilizes and preserves the much-desired energetic potential of thefinal nMx nanocomposite.

Our precise reaction uses a co-solvent system of tetrahydrofuran (THF)and toluene. We dissolve LiAlH₄ in THF. The toluene co-solvent is notcapable of dissolving the LiAlH₄ but serves as a solvent and heat sinkfor the reaction mixture when the reaction temperature is increased to85° C. The high boiling point of toluene (110° C.) is much larger thanthe boiling point of THF (66° C.), which is expected to boil offpartially even under reflux at 85° C. The volume to volume ratio oftoluene to THF is about 5.8 to 1 in the co-solvent mixture. The LiAlH₄powder is added first to the reaction flask followed by the co-solvents.When adding the co-solvents, the toluene is added first followed by theTHF.

The passivation agent is added 10 minutes after the addition of thetitanium isopropoxide solution is completed. It is an embodiment of thepresent invention wherein the full reaction time is about 40 minutes toabout 2 hours. The reaction starts when the nanoscale organic layer isadded to the reaction mixture, and the reaction ends when the reactionmixture is put under vacuum boil.

The molar ratio (moles of elemental Al nanoparticles and Li₃AlH₆nanoparticles divided by the moles of nanoscale organic layer) differsbetween nMx iterations. The nMx cores are composed of 2 moles ofelemental Al nanoparticles for 1 mole of Li₃AlH₆ nanoparticles. FornMx₁₂, the molar ratio of nMx (Al NPs and Li₃AlH₆ NPs) to stearylalcohol is 7.9:1. Therefore, the molar ratio of elemental Alnanoparticles to Li₃AlH₆ nanoparticles to stearyl alcohol is 5.2:2.6:1.

For nMx₁₃, the molar ratio of nMx to oleic acid is also 7.9:1. FornMx₁₆, the molar ratio of nMx to capping agents is 6.3:1. For nMx₁₉, themolar ratio of nMx to capping agent is 49:1. This molar ratio is veryhigh due to the molecular weight of the PEG molecules. For nMx₂₀, themolar ratio of nMx to capping agent is 4.4:1. In nMx₁₁, the nanoscaleorganic layer is not a self-assembled monolayer but nMx₁₁ cores initiatea PIERMEN capping mechanism. So, the molar ratio of nMx₁₁ to epoxydecene(monomer) to octadiene (monomer) is 10:1:2.

Although nanocrystals of Li₃AlH₆ and Al metal are observed via a topdown synthesis, i.e. decomposing LiAlH₄ by high energy ball milling,using force to create our composite is problematic. Ball milling is amechanical process, where chemical reactions are carried out by strikingpowder reactants with fast moving heavy balls. Strikes from the ballsgrind down reactants forcing a chemical change.

Surface and interface contamination is a major concern fornanocrystalline materials made by high-energy ball milling. The forcefrom the striking balls causes surface interactions of nascentnanoparticles to cold weld the particles together, which makes anaggregate that is difficult or impossible to disrupt. The milling ballsthemselves can contribute to contamination as well in the reactantmaterials. Ambient gases (trace impurities such as O₂, N₂ in rare gases)are also problems. One can take precautions in reducing thesecontaminations, but, because there is no true control over the reactionor reaction species, other than controlling milling time, there is nocontrol on nanoparticle morphology, agglomerates, and residual strain onthe crystalline structures formed through force.

Cold welding reduces the surface area of the final ball milled material,thereby reducing the observed energy output of the same. Cold welding isan unavoidable side effect of ball milling. Cold welding not onlycreates a distribution of unwanted chemical species in the reactionvessel, but also contributes to a large distribution size of the finalproducts, where one can observe nanoparticles, microparticles, andspecies that are essentially bulk metals [13].

Ball milling removes our ability to properly isolate true Li₃AlH₆nanoparticles and elemental Al metal nanoparticles without impuritiesduring the decomposition of LiAlH₄. Ball milling would also remove ourability to control the particle size of our composite. Strikes from theballs would inevitably crack and damage our nanoscale organic layer usedto protect and preserve the composite. This would result in a pyrophoricmaterial that is unsafe for handling. It could also affect thecombustion properties of the composite material and if an oxide layerforms about the core metal surfaces, this could result in a noticeablereduction in the unique burning properties of our invention. Therefore,it is a preferred embodiment of the present invention for thedecomposition of LiAlH₄ to be carried out via the bottom up reactions asdetailed below.

Catalytic Decomposition of LiAlH₄ to Create Nanoparticles

It is an embodiment of the present invention to add an alkoxide catalystto the reaction vessel to facilitate LiAlH₄ decomposition, which ensuresthat a sufficient number of both nanoparticles are created. We preciselypush and pull between reaction temperature, reaction time, and catalystamount to create a system that holds LiAlH₄ decomposition at the firstreaction step, where the resulting invention includes the two distinctnanoparticles, an amount of Ti metal, and a nanoscale organic layer forpassivation. The alkoxide or Ti catalyst for the present invention mayinclude, without limitation, a titanium(IV) compound, a titanium(IV)tetraalkoxylate, such as titanium(IV) isopropoxide, or a titanium(IV)tetraaryloxylate, or any combination thereof. However, it is anembodiment of the present invention where the alkoxide catalyst istitanium isopropoxide (Ti(O^(i)Pr₄, 97%).

Although ball milling will not give the high energy nanoparticles of thepresent invention, the technique lends insight into: 1.) the stabilityof LiAlH₄, 2.) the difficulty of using alkoxide catalysts with ballmilling, 3.) the sensitivity of Li₃AlH₆, and 4.) a possible explanationas to why there are trace amounts of Ti metal in our final compositeabsent cold welding and traditional alloying methods at the nanoscalelevel brought on by ball milling [6, 14, 15].

Ball milling studies indicate that, without a catalyst, LiAlH₄decomposition is difficult to achieve. The preferred catalyst for LiAlH₄decomposition via ball milling is a Ti halide. When an alkoxide is usedas a catalyst for this decomposition, impurities are observed [6]. Incomparison, the present invention cannot use Ti halide catalysts such asTiCl₄ due to the formation of chloride impurities during the reaction.

Catalytic decomposition of LiAlH₄ via ball milling shows that shortgrind times are necessary to ensure that newly formed Li₃AlH₆ does notfurther decompose into the second and third decomposition reactions andthat Ti alkoxide catalysts are detrimental to ball milling LiAlH₄, and,as such, Ti halides are the preferred catalysts for the ball millingexperiments [14].

Without the use of a catalyst, the decomposition of LiAlH₄ is arelatively slow reaction [14]. The method of making the presentinvention is a delicate push and pull between reaction temperature,reaction time, and catalyst amount used to create a system that holdsthe decomposition of LiAlH₄ to its first reaction step, where we createnanoparticles of both Li₃AlH₆ and elemental Al metal. The reaction isperformed below 100° C. to stop Li₃AlH₆ from further decomposition.

Not to be bound by theory, but, the true nature of Ti's catalytic effecton metal hydride decomposition is open for debate. For the presentinvention, Ti alkoxides are more like nanoparticle initiators, where thealkoxide reacts with LiAlH₄ to form molecular seeds by which thenanoparticles grow and where there are Ti remnants associated with themetals surfaces of both Li₃AlH₆ and elemental Al nanoparticles.

With the catalytic decomposition of NaAlH₄ with TiCl₄ by ball milling,Balema et al. observed a nascent Ti-Alloy phase form between Ti and Al[15]. If this true, then it is possible that unbound Ti from ouralkoxide catalyst could readily bind to the highly reactive surfaces ofour core nanoparticles before passivation with the nanoscale organiclayer. We propose that Ti—Al and Ti—Li₃AlH₆ bonds form in ournanocomposite at about 0.5% wt to about 1.0% wt of Ti metal in our finalcomposite.

nMx and the Importance of Passivation

The present invention discloses a singular material that is ananocomposite made of elemental aluminum nanoparticles, lithium aluminumhexahydride nanoparticles, an amount of Ti metal, and a nanoscaleorganic layer. We named this composite material nMx, which is air stableand protects and preserves the combustion properties of the compositeisolated from the first reaction step of LiAlH₄ decomposition. Wecreated a range of composites, nMx₁₀-nMx₂₀, based on the capping agentsused to passivate their surfaces.

In our reactions, when we passivate the core nanoparticles, we caneither use monomeric organic materials that self-assemble about thesurfaces of the nanoparticles or organic polymers that form a matrixabout the same. Monomers passivate the outer surfaces of the corenanoparticles and then polymerize on nascent nanoparticle surfaces.Passivating with monomers may (in the case of dienes) or may not (in thecase of fatty acids or alcohols) polymerize. If polymerization ensues,then the resulting polymer caps protect the underlying core material.However, the actual act of passivation can still be done by either amonomer type material or a polymeric type material. Nanoscale organiclayers that are epoxyalkenes and alkadienes form monolayers around thenanoparticles (molecules that are tethered to the nanoparticle surface,but are only weakly interacting with each other through intermolecularforces).

Passivation of our nanoparticle surfaces serves multiple purposes. Itcontrols particle size and distribution, prevents aggregation to keepthe core metals as isolated nanoparticles, passivation blocks impuritiesthat may form on particle surfaces, controls morphology and shape of thenanoparticles, and gives air stability, thereby getting rid of unwantedburning in ambient conditions. It is an embodiment of the presentinvention where the shape of the nanoparticles are a function of thepassivation agent used and the nanometer scale. The shapes range fromequant to 1 dimensional structures and may be spheroidal to rod shapedas well.

Elemental Al and Li₃AlH₆ nanoparticles are very sensitive and dangerousto work with. In their unpassivated states, these particles are highlyreactive and will spontaneously ignite and burn in ambient conditions.Because of the danger related to the core metals' high reactivity, ournanoparticle surfaces are altered to ensure air stability and removesthe possibility of flammability and pyrophoricity in air over a periodof time. This makes nMx safe to handle in air and to transport for usein applications.

Many passivation strategies have been reported. For micron-sizedparticles, simple oxide passivation may be useful since an oxide coatingof tens of nanometers up to hundreds of nanometers thick can account foronly a few percent or less of the total particle mass. For largerparticles, alternatives to oxide passivation of aluminum that provideincreased energy content include graphite, polymer, or transition metalcoatings.

For nanoscale particles, Jouet and coworkers reported nano-Alstabilization with perfluorocarboxylic acid monolayer coatings whileFoley and coworkers reported effective transition metal capping ofnano-aluminum [16, 17]. Additional metal coating and passivationtechniques would be a great advantage. However, most passivationtechniques for Al nanoparticles are very expensive, are not scalable formass production levels, and lack the chemistry needed to keep thepassivated particles stable in air for more than a few hours.

nMx Air Stability '& Air Sensitivity

It is an embodiment of the present invention where the highly reactiveLi₃AlH₆ nanoparticles and the elemental Al nanoparticles are safe tohandle in air without the concern of immediate combustion with ambientmoisture or oxygen while transporting them for use in otherapplications. However, as we measure the energetic properties of ourinvention with different passivating agents, we observe that airstability and sensitivity strongly correlate with the oxygen atomcontent of the nanoscale organic layer. nMx's air stability fluctuatesas the oxygen atom content increases in the same.

FIG. 3 depicts a chart showing a relationship between the oxygen atomcontent of the nanoscale organic layer and air stability fornMx₁₀-nMx₂₀, where the increasing nMx subscripts correspond to increasedoxygen content in the nanoscale organic layer about the core metals. Thex-axis of FIG. 3 shows the variation in passivation agents. The y-axisof FIG. 3 represents the total mass fraction of organic in thenanocomposite. At one end, nMx₁₀ has a polymerized organic hydrocarboncap. The O atom mass percentage is 0%, and, at the other end, nMx₂₀, hasa polyethylene oxide capping structure, with an O atom mass percentageof ˜42%.

From FIG. 3, variations between nMx₁₀ and nMx₂₀ have intermediate O atommass percentages between 0% and 42%. The maximum oxygen atom content weobserve for a stable composite is for nMx₂₀, with 42% by mass oxygencontent in the passivating agent. In contrast, the oxygen atom contentfor nMx₁₂ and nMx₁₃ (approximately 6% and 12%, respectively) leads tothe formation of surface aluminum oxygen bonds throughout the compositethat renders the material fully air stable. However, it is an embodimentof the present invention where the nanoscale organic layer is locatedabout the surfaces of the composite, with a mass percentage from about25% to about 70% of the total mass. One mass fraction of organic canvary down to 25% for air stability of the nanocomposite. Hot spots arenot observed with nMx₁₂ that would lead to spontaneous burning and theenergy density of the material is at a maximum (−38 kJ/g for nMx₁₂).

The metal nanoparticles of nMx₁₂ through nMx₂₀ neither spontaneouslyignite nor rapidly react with ambient oxygen in air, primarily from H₂Oand O₂. nMx₁₂ through nMx₂₀ are all air stable when using the methods ofmaking disclosed herein. nMx₁₀ to nMx₂₀ vary in both air stability andair sensitivity. nMx₁₀ is unstable in air, where large quantities ofnMx₁₀ have pyrophoric hot spots that spontaneously ignite.

nMx₁₁ is not as reactive as nMx₁₀, but, in large quantities, nMx₁₁displays pyrophoric behavior, making large quantities of the materialair unstable. nMx₁₀ and nMx₁₁ are generally unsafe to handle in anyhumid environment. In summary, nMx nanocomposites below nMx₁₂ are notair stable. The reactivity of nMx with air is very high with nMx₁₀,decreases to a minimum at nMx₁₂ and nMx₁₃, and slowly increases as onemoves left from nMx₁₃ across FIG. 3 to nMx₁₀ and nMx₂₀.

For the present invention, air sensitivity is a similar but differentproperty than air stability. Air sensitivity is the tendency for anenergetic material to slowly react in air (primarily with water andmolecular oxygen) to lose energy density. This loss of energy densitymay take place over the timescale of fractions of an hour, days, weeks,or longer periods of time.

The air sensitivity of nMx is at a minimum for nMx₁₂ and nMx₁₃. Thesematerials are air stable and have low air sensitivity, losing energydensity over longer periods of time, depending on air humidity. The airsensitivity increases moving from nMx₁₂ and nMx₁₃ to nMx₁₉ and nMx₂₀.The nanoscale organic layer for both nMx₁₉ and nMx₂₀, for example PEGcapping groups, are more hydrophilic. This hydrophilicity results inmore atmospheric water accessing the metal cores of nMx₁₉ and nMx₂₀,thus reducing the energy density more rapidly in air and indicating thatthey are more air sensitive.

The combination of the elemental Al nanoparticles and the Li₃AlH₆nanoparticles are in an approximately equal amount by mass to the entirenanocomposite. However, when the composite's aluminum nanoparticles havedimensions less than 50 nm, the singular composite with organic cappingcontent <25% is not air stable, i.e. the composite of Li₃AlH₆nanoparticles and elemental aluminum nanoparticles with the cappingagent is less stable when the aluminum nanoparticles are smaller thanabout 50 nm and where the capping agent is less than 25% of the totalmass.

As the oxygen atom content for the capping agent increases, the airstability of the nMx continue to evolve. Due to increased airsensitivity, the air stability of nMx₁₉ and nMx₂₀ decrease. The increasein O-atom content of the organic cap increases the accessibility ofatmospheric water to the Al-containing nanoparticles. This accessibilitylimits the long-term air stability. The less oxygen in the organic layerthe higher the nMx combustion enthalpy, which proceeds by way of thefollowing combustion reaction:2Al(NPs)+Li₃AlH₆(NPs)+NSOL+O₂(g)→3/2Li₂O(s)+3/2Al₂O₃(s)+12CO₂(g)+15H₂O(g),where the NSOL may include, without limitation, a poly(alkadiene), apoly(epoxyalkene-co-alkadiene), a fatty alcohol, a fatty acid, apolyethylene glycol (either with or without substitution and having amolecular weight from about 200 g/mol to about 6000 g/mol).

Air stability is measured for both nMx₁₂ and nMx₂₀. Each sample is apowder form and left exposed to the ambient air in a pan, where thehumidity was greater than or equal to 55% relative humidity. Table 1shows air stability for nMx₁₂ and nMx₂₀. After exposure to ambient air,energy densities are measured against time, where all bomb calorimetrydata is acquired with a Parr1341 Plain Jacket calorimeter.

All nMx samples are ignited under 20 atm of oxygen gas within the Parr1108 Oxygen Bomb. The sample is placed into a stainless steel capsule(Parr 43AS), and the sample is ignited with a ˜10 cm nickel alloy fusewire (Parr 45C10). The electric current used to ignite the sample isprovided by a Parr 2901EB Ignition Unit. The temperature is monitoredwith a digital thermometer (Parr 6775). The assembled bomb calorimetercontaining the sample is brought to thermal equilibrium with the aid ofmechanical stirring. Once the calorimeter reaches thermal equilibrium,the sample is ignited to raise the temperature, and the calorimeter isleft to stir until thermal equilibrium is established.

The heat of combustion is acquired from the rise in temperature, theweight of the sample, and the premeasured calorimeter constant value.For the air stability measurements, the sample is placed on a 102 mmdiameter Al dish and rests in the air for ˜20-30 minutes with a relativehumidity of ˜55%. It is an embodiment of the present invention where thenanocomposite air stability is measured by an 10% decrease in measuredenergy density for a period of 8 hours when the nanocomposite is exposedto ambient air and remains non-pyrophoric.

TABLE 1 The change in energy density against time as a measure of airstability for nMx₁₂ and nMx₂₀ over a duration of 8 hours. nMx₁₂ nMx₂₀Energy Density Energy Density (kJ/g) (kJ/g) Time (Hours) −38 −28 0 −37−26 0.5 −35 −25 2 −35 −24 4 −34 −21 8

nMx₁₉ and nMx₂₀ as a Thermite

Another significant change that occurs with the increase in oxygen atomsfor the nanoscale organic layer at nMx₁₉ and nMx₂₀, as made by ReactionNo. 6 below, is that both nanoparticles display thermite behavior. Weobserve that both nMx₁₉ and nMx₂₀ carry out self-sustaining combustionin an inert gas environment, such as argon, and even carries outself-sustaining combustion in vacuo, where our composite burns in theabsence of any other oxidizer. Not to be bound by theory, but we believethat the unexpected behavior for both nanothermites is due to the PEGorganic matrix serving as an effective oxidizer for the elementalaluminum nanoparticles and the Li₃AlH₆ nanoparticles.

Both nanothermites may combust via the following reactions. We list theprimary thermite reaction in the absence of O₂ for nMx₂₀ (and nMx₁₉) as:2Al(NPs)+Li₃AlH₆(NPs)+6(C₂H₄O)_(n)→3/2Li₂O(s)+3/2Al₂O₃(s)+12C(s)+15H₂(g),where ΔH°_(reaction)=−8.03 kJ/g for nMx₂₀. Further energy release canoccur when the released hydrogen gas oxidizes, which we have observedduring oxidation of these systems in air:H₂(g)+½O₂(g)→H₂O(l),where ΔH°_(reaction)=−143 kJ/g H2.

The other possible pathway includes:2Al(NPs)+Li₃AlH₆(NPs)+6(C₂H₄O)_(n)→3LiAlO₂(s)+12C(s)+15H₂(g),where ΔH°_(reaction)=−642.5 kJ/mol=−1.73 kJ/g for nMx₂₀.

Based on the thermodynamic date taken from Table 2, we calculate theenthalpy of reaction as ΔH°_(f)=−2988 kJ/mol for the reactionstoichiometry as written. This large reaction enthalpy is driven by thehighly reducing and reactive natures of the composite reactants workingin tandem to facilitate unique burning. We observe copious amounts ofsoot and hydrogen gas released in this reaction, verifying the productsof nMx₂₀ thermite reaction. The combination of the aluminumnanoparticles and Li₃AlH₆ nanoparticles gives a high energy densitymaterial with an extremely high burn rate. The close interfacial contactbetween the oxygen atoms of PEG and the aluminum and lithium aluminumhexahydride cores is present, allowing for a fast-kinetic redoxreaction. In this material, the ether becomes a significant oxidizer.

TABLE 2 Thermodynamic data relevant to the nMx₂₀ nanothermite reaction.Enthalpy of Component formation (ΔH°_(f) kJ/mol) Li₃AlH₆ −332.2 Li₂O−131.7 Al₂O₃ −1669.8 PEG (per monomer unit {C₂H₄O}) 103 Elemental Al, C,& H₂ 0

Table 3 lists the % oxygen by mass for various nMx iterationsnMx₁₂-nMx₂₀ and their corresponding combustion enthalpies as measured bybomb calorimetry. For simplicity nMx₁₄, nMx₁₅, nMx₁₇, and nMx₁₈ are notlisted. As the extent of oxidation of the organic capping layerincreases, the enthalpy of combustion of the system decreases, asexpected. However, as not to be bound by theory, nMx₂₀ includes pure PEG(no carbon side chains) and derives its large energy density from thenanoparticle cores. The range of physical parameters that providenanothermite behavior for nMx₂₀ includes, but are not limited to, theelemental Al nanoparticles having particle diameters in the range ofabout 7 nm to about 100 nm, the Li₃AlH₆ nanoparticles having particlediameters in the range of about 15 nm to about 100 nm, the PEG cappingagent having a molecular weight range from about 150 amu to about 10,000amu, the composite to PEG mass ratio being from about 1:10 to about 4:1,and the elemental aluminum nanoparticles and the Li₃AlH₆ nanoparticleshaving a mass ratio from about 10:1 to about 1:3. It is a preferredembodiment of the invention wherein the PEG capping agent has amolecular weight of about 194 amu for the passivation of nMx₂₀.

TABLE 3 lists iterations nMx₁₂-nMx₂₀, where the % oxygen by mass isgiven for various nMx iterations according to the capping agent alongwith the corresponding combustion enthalpies, ΔH°_(combustion), asmeasured by bomb calorimetry. Formulation nMx₁₂ nMx₁₃ nMx₁₆ nMx₁₉ nMx₂₀% O cap by mass 8% 12% 25% 37% 41% ΔH°_(combustion) −38 kJ/g −35 kJ/g−32 kJ/g −27 kJ/g −28 kJ/g

Reaction No. 6 below represents the first aluminum-based nanothermitewith an organic ether as the oxidizing agent. Organic explosives(typically ring strained organic compounds with covalently bonded nitrogroups) are known to combust in vacuum. Aluminum nanoparticlescontaining nanothermites that are known in the literature typicallycontain a metal oxide (such as copper (I) oxide or molybdenum (VI)oxide) that serves as the oxygen source.

Our prior work on polyether-coated aluminum nanoparticles, see US Pat.Pub. No. 2012/0009424 as filed by Jelliss et al. does not displaythermite behavior, where this publication does not disclose nMx asclaimed herein [18]. We did not see thermite behavior with thepolyether-coated aluminum nanoparticles due to: (1) the absence ofLi₃AlH₆ nanoparticles from the composite and (2) the extra organic sidechains that were present on the prior materials that were produced,greatly reducing the oxygen content in the organic cap. Those extracarbon atoms on the side chain are known to significantly slow orinhibit these types of reactions—hence the thermite behavior is notobserved when the PEG cap has an organic side chain. Therefore, priorproduced materials were not thermites.

The reaction for nMx₂₀ uses an organic ether as the thermite oxidant.Ethers are generally considered to be relatively unreactive and they arenot considered to be oxidizing agents under normal chemical conditions.This is one reason organic ethers have not been investigated asnanothermite oxidizers. nMx iterations with capping agents having loweroxygen atom content are better suited to applications as a propellantdue to their increased air stability, better compatibility with binders,and higher overall energy density. Our composite has shown uniqueburning characteristics and energy outputs that could lead to Improvedspecific impulses for engines needing a high-energy output with a highervelocity of released gases and improved mass flow.

The energetic properties of each nMx composite depend on the percentageof oxygen available in the organic nanoscale layer used when passivatingour nanoparticles. More specifically, the combustion properties of thematerial track to the oxygen atom content in the organic matrix. As theoxygen atom content increases in the capping agent, nMx's air stabilitychanges.

For nMx₁₀ and nMx₁₁, the less or non-air stable iterations of nMx, thecapping agents are selected from alkadienes (nMx₁₀) or a mixture of anepoxyalkene and an alkadiene (nMx₁₁), including but not limited to1,7-octadiene, 1,9-decadiene, myrcene, or 1,13-tetradecadiene,epoxyhexene, epoxyheptene, epoxyoctene, epoxynonene,epoxydecene,epoxyundecene, epoxydodecene,1,3-butadiene, isoprene,2-methyl-1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene,2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-pentadiene,1,3-hexadiene, 2-methyl-1,3-hexadiene, 1,3-heptadiene,3-methyl-1,3-heptadiene, 1,3-octadiene, 3-butyl-1,3-octadiene,3,4-dimethyl-1,3-hexadiene, 3-n-propyl-1,3-pentadiene,4,5-diethyl-1,3-octadiene, 2,4-diethyl-1,3-butadiene,2,3-di-n-propyl-1,3-butadiene, and 2-methyl-3-isopropyl-1,3-butadiene,and combinations thereof. Not to be bound by theory, but theseparticular capping agents have an oxygen content that ranges from about0% to about 7% and only forms minimal aluminum oxygen, Al—O, bondsduring the passivation process by reaction with epoxide.

Instead, passivation of nMx₁₀ and nMx₁₁ occurs via polymerization orco-polymerization of the alkadienes or a mixture of an epoxyalkene andan alkadiene to form a matrix about the Al nanoparticles and Li₃AlH₆nanoparticles. It is believed that the reductive nature of the elementalaluminum nanoparticles causes the carbon carbon double bonds of thealkadiene or the epoxyalkene to cleave, which promotes polymerization orcopolymerization about our composite core material. In some embodiments,the polyolefin polymerization is thermally promoted. In addition, webelieve that surface hydrides are not able to initiate polymerization ofcertain capping agents, leaving those areas on the surface unpassivated.Because of the low oxygen content and lack of substantial aluminumoxygen bonding at the surfaces of our composite, this polymerizationscheme leaves portions of the Li₃AlH₆ nanoparticles exposed to ambientreactions, which can induce unwanted burning across the entire mixture.

In some embodiments, these organic polymers form a hydrophobic layeraround the nanomaterial such that the polymer hinders the reactivity ofthe same. In some respects, capping the nanoparticles with an organicpolymer hinders the formation of aluminum oxide leading to a morereactive nanomaterial. Without being bound by theory, the hydrophobicpolymer may delay reactive molecules such as water and oxygen fromreaching the surface of the nanomaterial. In some embodiments, thenanoparticles are capped with alkyl-substituted epoxides. In someembodiments, these polymers are formed from the polymerization of thealkadienes.

It is an aspect of the present invention wherein our singular material,being a composite of both Li₃AlH₆ nanoparticles and elemental Alnanoparticles, are both passivated with a variety of organic orinorganic compounds. In some embodiments, capping is achieved usingtransition metal ions or the use of perfluoroalkylcarboxylic acids asshown by Foley, et al., 2005 and Jouet, et al., 2005, both of which areincorporated herein by reference [16, 17]. The use of polymers to act asa capping agent is also considered. Other capping agents include withoutlimitation fatty acids, fatty alcohols, poly(alka-dienes),poly(epoxyalkene-co-alkadiene), polyethylene glycol (PEG), or anycombinations thereof.

For nMx₁₂, capping agents for passivation may include, but are notlimited to, fatty alcohols being tert-butyl alcohol, tert-amyl alcohol,3-methyl-3-pentanol, ethchlorvynol, 1-octanol (capryl alcohol),(1-nonanol), 1-decanol (decyl alcohol, capric alcohol), undecyl alcohol(1-undecanol, undecanol, hendecanol), HTPB, lauryl alcohol (dodecanol,1-dodecanol), tridecyl alcohol (1-tridecanol, tridecanol,isotridecanol), myristyl alcohol (1-tetradecanol), pentadecyl alcohol(1-pentadecanol, pentadecanol), cetyl alcohol (1-hexadecanol),palmitoleyl alcohol (cis-9-hexadecen-1-ol), heptadecyl alcohol(1-n-heptadecanol, heptadecanol), stearyl alcohol (1-octadecanol),nonadecyl alcohol (1-nonadecanol), arachidyl alcohol (1-eicosanol),heneicosyl alcohol (1-heneicosanol), behenyl alcohol (1-docosanol),erucyl alcohol (cis-13-docosen-1-ol), lignoceryl alcohol(1-tetracosanol), ceryl alcohol (1-hexacosanol), 1-heptacosanol,montanyl alcohol, cluytyl alcohol, or 1-octacosanol, 1-nonacosanol,myricyl alcohol, melissyl alcohol, or 1-triacontanol, 1-dotriacontanol(lacceryl alcohol), geddyl alcohol (1-tetratriacontanol), cetearylalcohol or any combinations thereof, or using enols for crosslinkingwith aladienes enols, or enoic acids.

For nMx₁₃, capping agents for passivation may include, but are notlimited to, carboxylic (fatty) acids being butyric acid [CH₃(CH₂)₂COOH],valeric acid [CH₃(CH₂)₃COOH], caproic acid [CH₃(CH₂)₄COOH], enanthicacid [CH₃(CH₂)₅COOH], caprylic acid [CH₃(CH₂)₆COOH], pelargonic acid[CH₃(CH₂)₇COOH], capric acid [CH₃(CH₂)₈COOH], undecylic acid[CH₃(CH₂)₉COOH], lauric acid [CH₃(CH₂)₁₀COOH], tridecylic acid[CH₃(CH₂)₁₁COOH], myristic acid [CH₃(CH₂)₁₂COOH], pentadecylic acid[CH₃(CH₂)₁₃COOH], palmitic acid [CH₃(CH₂)₁₄COOH], margaric acid[CH₃(CH₂)₁₅COOH], stearic acid [CH₃(CH₂)₁₆COOH], nonadecylic acid[CH₃(CH₂)₁₇COOH], arachidic acid [CH₃(CH₂)₁₈COOH] or any combinationsthereof, or using enols for crosslinking with aladienes enols, or enoicacids.

For nMx₁₄-nMx₁₈, capping agents for passivation include, but are notlimited to, a mixture of a fatty acid, fatty alcohol, polyethylenealcohol (PEG), and an alkadiene. Fatty acids include the list of acidsused to passivate nMx₁₃ or any combinations thereof. The fatty alcoholsinclude the list of alcohols used to passivate nMx₁₂ or any combinationsthereof. The alkadienes include the list of alkadienes used to passivatenMx₁₀ and nMx₁₁ or any combinations thereof.

For nMx₁₉ and nMx₂₀, capping agents for passivation include, but are notlimited to, PEG, PEO, tetraethylene glycol, or triethylene glycol allhaving various molecular weights.

Reagents & Materials for nMx Reactions

This is a list of the chemicals used to make any of nMx₁₁-nMx₂₀: Lithiumaluminum hydride (LiAlH₄, powder, reagent grade, 95%), titanium (IV)isopropoxide (99.999% trace metals basis), 1,7-octadiene (98%),1,9-decadiene (98%), 1,13-tetradecadiene (90%), toluene (anhydrous,99.8%), tetrahydrofuran (THF, anhydrous, 99.9%, inhibitor-free),polyethylene glycol (PEG), tetrethylene glycol, triethylene glycol,stearyl alcohol, and stearic acid were all purchased from Sigma Aldrich.Anhydrous diethyl ether was purchased from J. T. Baker. Toluene and THFwere distilled over sodium metal and potassium metal, respectively, toremove any trace oxygen and water. Diethyl ether and methanol weredistilled over 4 Å molecular sieves. All alkenes were subjected tonumerous freeze-pump-thaw cycles to remove any oxygen present.Generally, titanium (IV) alkoxide was dissolved in toluene to create adilute (millimolar range) solution. Both LiAlH₄ and the titaniumcatalyst were stored under argon atmosphere to prevent oxygen/waterexposure.

Reaction No. 1: Creating nMx₁₀

Reaction No. 1 begins by adding LiAlH₄ (0.246 g, 6.48 mmol) to around-bottom Schlenk flask and dissolving the ternary metal hydride ineither THF or diethyl ether to create a 1.0 M solution. Following theaddition of 20 mL toluene, the reaction mixture is heated to 85° C.using a J-KEM Model Apollo dual channel temperature controller. Uponreaching 85° C., 16 μL Ti(O^(i)Pr)₄ is added followed by the immediateaddition of the capping agent (octadiene, decadiene, or tetradecadiene;10:1 Al:capping agent molar ratio). The reaction mixture can stir underreflux for 30 minutes, and all solvents are then removed in vacuo.

The nanocomposite is formed from the decomposition of LiAlH₄ in thepresence of Ti(O^(i)Pr)₄ at 85° C. in either THF or diethyl ether.However, the reaction temperature can be from about 75° C. to about 150°C. The temperature is selected to stop the decomposition of LiAlH₄ atthe first reaction step to produce Al NPs, Li₃AlH₆ NPs, and H₂ gas. Notethat the composite material is co-formed (˜50 weight % aluminum:lithiumalanate NPs) in the LiAlH₄ decomposition reaction. In some embodiments,the method further comprises heating the solution for a time of about 1minute to about 3 hours. In some embodiments, the time is about 30minutes. Dienes, such as 1,7-octadiene, 1,9-decadiene, and1,13-tetradecadiene, were used as passivating agents since the uncappedparticles were pyrophoric in air. All reactions were performed on aSchlenk line under argon atmosphere.

In some embodiments of the present invention, the composite has a ratioof Al nanoparticles to Li₃AlH₆ nanoparticles from about 5:1 to about1:5, and in some cases, the ratio is about 1:1. Also note that thecomposite material, being a mixture of Al nanoparticles and Li₃AlH₆nanoparticles, comprise a core diameter from about 15 nm to about 60 nm.However, the optimal diameter for all formed nanospheres should have acore diameter from about 35 nm to about 55 nm.

It is an aspect of the present invention where the method includesadding 0.1 equivalents of capping agent per equivalent of aluminum. Thecapping agents for the above reaction may include without limitation analkene(C≤30), substituted alkene(C≤30), an alkene(C≤18), analkene(C≤14), an epoxide(C≤30), or a substituted epoxide(C≤30), wherethe capping agent may undergo polymerization to form a matrix likecoating across all nanoparticle surfaces. In other embodiments of thepresent invention, the alkene contains two or more carbon carbon doublebonds. In some embodiments, the capping agent is 1,7-octadiene,1,9-decadiene, myrcene, or 1,13-tetradecadiene.

In some embodiments, the solvent is heated to reflux. In someembodiments, the titanium compound is added after the solution hasreached the temperature from about 70° C. to about 100° C. In someembodiments, the method is performed under an inert atmosphere. In someembodiments, the inert atmosphere is nitrogen gas or a noble gas. Insome embodiments, the inert atmosphere is argon. In some embodiments,the method further comprises adding a capping agent to the reaction.

In some aspects of the present invention, the solvent is an organicsolvent, non-limiting examples being ether(C≤12), tetrahydrofuran ordiethyl ether, arene(C≤12), toluene, a mixture of toluene andtetrahydrofuran, a mixture of toluene and diethyl ether, or anycombinations thereof.

In some aspects of the present invention the catalyst may be, withoutlimitation, a titanium(IV) compound, a titanium(IV) tetraalkoxylate,such as titanium(IV) isopropoxide, or a titanium(IV) tetraaryloxylate orany combinations thereof.

In addition, atoms making up aluminum nanoparticles, the Li₃AlH₆nanocomposites, and aluminum nanocomposite materials are intended toinclude all isotopic forms of such atoms. Isotopes, as used herein,include those atoms having the same atomic number but different massnumbers. By way of general example and without limitation, isotopes ofhydrogen include tritium and deuterium, and isotopes of carbon include¹³C and ¹⁴C. Isotopes of lithium and aluminum are also contemplated inthe compounds so long as the isotopes are stable.

Reaction No. 1 and its corresponding data is our first attempt to makethe present invention. This reaction is disclosed in U.S. patentapplication Ser. No. 14/259,859, to which the current application claimspriority. nMx₁₀, although passivated, displays unwanted burning inambient conditions. Those in the art that wish to practice nMx₁₀ pleasetake precautions against unpredictable burning events, as the cores arenot as air stable as the subsequent iterations nMx₁₁-nMx₂₀. Not to bebound by theory, but the instability of nMx₁₀ in ambient conditions maybe due to the type of capping agents used in passivation. The method ofmaking nMx₁₀ has organic capping agents, including but not limited to,an alkadiene such as myrcene or other alkadienes from C₆ to any higheralkadiene, which results in polymerization and only partialstabilization of the core metal nanoparticles.

nMx₁₀ capping agents may include without limitation: dienes, such as1,7-octadiene, 1,9-decadiene, and 1,13-tetradecadiene, myrcene, anyalkene containing at least two carbon-carbon double bonds greater than 4carbons and less than 30 carbons, an alkene(C≤30), substitutedalkene(C≤30), an alkene(C≤18), an alkene(C≤14), an epoxide(C≤30), or asubstituted epoxide(C≤30), where the capping agent may undergopolymerization to form a matrix like coating across all nanoparticlesurfaces.

Powder X-Ray Diffraction for nMx₁₀

All PXRD measurements were made using a Rigaku Miniflex 600 equippedwith a Cu source operated at 40 kV and a scintillation counter detector.All assignments were made via comparison with the appropriate patternsfrom the ICDD Crystallographic Database. Powder X-ray diffraction (PXRD)of the resulting grey powder shows the presence of 2 different phases inthe resulting sample: face-centered cubic aluminum (fcc Al) andmonoclinic lithium hexahydride (Li₃AlH₆).

Estimated NP core sizes and d-spacings from PXRD analysis are presentedin Table 4. The crystalline Al NP cores were ˜29 nm in diameter asdetermined from Scherrer analysis of the (111), (200), (220), and (331)diffraction peaks. The Li₃AlH₆ nanoparticles also appear to benanocrystalline with NP core diameters between ˜23-36 nm. The estimatedd-spacings are also in agreement with those reported for Li₃AlH₆ byBastide et al., which is incorporated herein by reference [23].

Elemental analysis of the nanocomposite using PDXL software provided byRigaku indicates 51% by mass of the crystalline nanocomposite materialis comprised of Al whereas the remaining 49% is comprised of Li₃AlH₆.These mass percentages are expected based on the stoichiometry presentedin Reaction 1. These mass percentage values do not account for thepresence of organic cap at the NP surface however. We can vary theparticle diameters by (a) allowing the reaction to proceed for a longertime prior to addition of capping agent and (b) addition of polymers tothe solution during reaction to increase viscosity. Our Al nanoparticlesizes can be varied from 10 nm to around 75 nm by adjusting theseparameters.

TABLE 4 PXRD data for nMx₁₀, where estimated crystalline core sizes andd-spacing values for various lattice planes of fcc Al nanoparticles andmonoclinic Li₃AlH₆ nanoparticles are presented. 2θ(°) Material (LatticePlane) Crystalline Size (nm) d-spacing 21.9 Li₃AlH₆ (110) 36 0.406 22.5Li₃AlH₆ (012) 35 0.395 31.7 Li₃AlH₆ (202) 32 0.282 38.4 Al (111) 200.234 39.8 Li₃AlH₆ (104) 33 0.226 44.7 Al (200) 28 0.202 50.6 Li₃AlH₆(13-2) 28 0.180 51.5 Li₃AlH₆ (12-4) 28 0.177 60.5 Li₃AlH₆ (21-5) 230.153 61.4 Li₃AlH₆ (32-2) 36 0.151 62.6 Li₃AlH₆ (11-6) 28 0.148 65.1 Al(220) 28 0.143 66.1 Li₃AlH₆ (404) 34 0.141 78.2 Al (311) 32 0.122 82.4Al (222) 35 0.117

Although lithium hydride (LiH) is a byproduct of the proposed breakdownof LiAlH₄, no LiH is observed via PXRD. While LiH is expected to have afcc crystal lattice similar to that of the fcc Al, the diffractionpattern that can be observed closely aligns with that expected for fccAl rather than LiH including exact d-space values corresponding to fccAl and a strong (111) diffraction peak that is weak for LiH.Furthermore, LiAlH₄ is not observed in the diffraction pattern either,indicating complete conversion to the nanocomposite product.

Fourier-Transform Infrared Spectroscopy for nMx₁₀

A Shimadzu model FTIR-8400S spectrometer equipped with an attenuatedtotal reflectance (ATR) attachment was used to collect all infraredspectroscopic data. All samples were dispersed in toluene prior toanalysis. Using Fourier-transform infrared spectroscopy (FTIR), thepresence of organic materials on the Al NP surface is noted by the C—Hstretching vibrations at ˜2970 cm⁻¹ and ˜2850 cm⁻¹. Since alkenes werechosen as the capping monomers for this material, C—H stretchingvibrations are expected. The IR spectrum shows no evidence of C═Cstretching supporting the conclusion that the reaction produced C═Cpolymerization thereby reducing the double bonds. PIERMEN(polymerization initiation by electron rich metal nanoparticles) whenusing alkenes as capping monomers for Al NPs prepared by alanedecomposition has been observed [19].

Transmission Electron Microscopy (TEM) of nMx₁₀

FIG. 21 depicts TEM images and electron diffraction patterns for nMx₁₀as acquired using a Philips EM430ST operated at 300 kV. Samples are caston Formvar grids. Image J software is used to estimate d-spacing valuesfrom the electron diffraction pattern. The TEM images indicate thenanoparticles are ˜50 nm in diameter. The nanoparticles also appear tobe enveloped within a polymer matrix, which is a result of the cappingmonomer, 1,7-octadiene. The cross-linked polymer layer well protects thecrystalline NP cores, with no visible evidence of an amorphous Al oxidelayer. The TEM images also reveal a homogenous mixture of Al NPs andLi₃AlH₆ NPs. The less dense spherical particles observed in the TEM aremost likely Li₃AlH₆ NPs. Spectroscopic data (FTIR) supports the presenceof polymeric hydrocarbons on the alanate NP surface as well.

TABLE 5 nMx₁₀ estimated d-spacing values for the rings resulting fromfcc Al nanoparticles. Ring d-spacing (nm) Material (Lattice Plane) 10.362 Li₃AlH₆ (012) 2 0.254 Al (111) 3 0.218 Al (200) 4 0.155 Al (220) 50.132 Al (331)

Similar observation was also noted in the obtained electron diffractionpattern (not shown). Table 5 presents aggregates data for defined ringswith d-spacings corresponding to those for fcc Al that were clearlydenoted. Our data showed more diffuse rings being visible; however,proper identification of those rings were difficult in that instance.Presumably, the diffuse rings were the result of monoclinic Li₃AlH₆. Anestimated d-spacing value of 0.362 nm was calculated for the innerdiffuse ring located closest to the electron beam (Ring 1). Withoutbeing bound by theory, the inner ring could be assigned to the (111)lattice plane of Li₃AlH₆; presumably, electron diffraction resultingfrom the (111) plane would be strongest. Although the diffuse ringscannot positively be identified, the extreme homogeneity of thenanocomposite is evident based on both the noticeable presence ofmultiple phases in both the electron diffraction patterns and in the TEMimages (FIG. 21).

Reaction No. 2: Creating nMx₁₁

Reaction No. 2 and its corresponding data relates to our process formaking and identifying nMx₁. It is an aspect of the present inventionwherein nMx₁₁ is produced by a bottom up synthesis that createsnanoparticles of both Li₃AlH₆ and elemental Al metal that are carefullysized and passivated at the controlled first reaction step of LiAlH₄decomposition, where the capping agent is a mixture of epoxydecene andan alkadiene. The combination of an epoxide and an alkadiene(1,7-octadiene has been demonstrated, but other alkadienes from C₆ toany higher alkadiene can also be used) results in polymerization andpartial stabilization of the metal cores that can be stated simply as:Core NPs+epoxydecene+alkadiene→nMx-poly(epoxydecene-co-alkadiene)+H₂(g)where the mixture of capping agents copolymerize to form a slightlyhydrophobic nanolayer about both core nanoparticles.

The following chemicals for making nMx₁₁ are purchased fromSigma-Aldrich and are as follows: Lithium aluminum hydride (LiAlH₄(95%)), titanium isopropoxide (Ti(O^(i)Pr₄, 97%), toluene (anhydrousgrade, 99.8%), tetrahydrofuran (THF, anhydrous grade, ≥99.9%,inhibitor-free), epoxydecene, and 1,7-octadiene.

The solvents toluene and THF are not distilled and are kept in aglovebox, since they are anhydrous. Before reaction, both the tolueneand the THF are deoxygenated by simply pumping their containers for 3cycles on a Schlenk line. The Ti(O^(i)Pr)₄ is placed in an air-freestorage flask and then freeze-pumped-thawed. All liquid reagents aretransferred to separate pre-heat dried, air-free flask inside theglovebox. The capping agents epoxydecene and 1,7-octadiene are degassedusing either freeze-pump-thaw cycles or by purging with an inert gassuch as Ar or N₂.

The entirety of Reaction No. 2 is performed on a Schlenk line underargon atmosphere. The co-solvent system of toluene and THF can heat forat time at 85° C. The co-solvents are then added to a round bottom airfree flask having LiAlH₄, where the metal hydride is dissolved in thestirring toluene and tetrahydrofuran mixture. Other ethers besidetetrahydrofuran can be used such as diethyl ether or 1,4-dioxane. Athermocouple is inserted into the reaction mixture to monitor thetemperature of the reaction.

Once the LiAlH₄ is added to the hydrocarbon-ether co-solvent system thereaction temperature is increased from about 100° C. to about 110° C.,or the reaction mixture can remain at about 85° C. with a heating mantlewhile stirring with a stir bar. In a separate air-free flask, thetitanium isopropoxide is dissolved in toluene to create a solution witha concentration of ˜10% v/v. Once the reaction mixture reaches from 85°C. to about 110° C., the titanium isopropoxide solution is added tocatalyze the decomposition of LiAlH₄.

The decomposition reaction is left heating and stirring for ˜10 minutesuntil the epoxydecene and 1,7-ocatdiene are added. Typical ratios of thecapping molecules are from 1:1 to about 2:1 for thealkadiene:epoxyalkene.

Once the epoxydecene and the 1,7-octadiene are added, the reactionmixture can react for a duration from about 0.5 hours to about 2 or morehours. After about a 2-hour reaction time, the solvent is removed byboiling in vacuo or can be removed by filtration or other methods. Theorganic content of the final nMx₁₁ is about 50% w/w. A theoretical yieldof 6 g of nMx₁₁ is produced.

Reaction No. 3: Creating nMx₁₂

Reaction No. 3 and its corresponding data relates to our process formaking and identifying nMx₁₂. It is an aspect of the present inventionwherein nMx₁₂ is produced by a bottom up synthesis that createsnanoparticles of both Li₃AlH₆ and elemental Al metal that are carefullysized and passivated at the controlled first reaction step of LiAlH₄decomposition, where the passivation agent is a fatty alcohol. It is anembodiment of the present invention wherein the capping agent is stearylalcohol and passivation is by way of aluminum oxygen bonding between theoxygen atoms available on the passivation agent and the surfaces of thealuminum nanoparticles and can be stated simply as:Core NPs+stearyl alcohol→nMx-stearyl alkoxy+H₂(g),wherein the organic layer binds to the composite through aluminum oxygenbonds thereby forming stearyl alkoxy at the composite's aluminumsurfaces.

The following chemicals for making nMx₁₂ are purchased fromSigma-Aldrich and are as follows: Lithium aluminum hydride (LiAlH₄(95%)), titanium isopropoxide (Ti(O^(i)Pr)₄, 97%), toluene (anhydrousgrade, 99.8%), tetrahydrofuran (THF, anhydrous grade, ≥99.9%,inhibitor-free), and stearyl alcohol.

The solvents toluene and THF are not distilled and are kept in aglovebox, since they are anhydrous. Before reaction, both the tolueneand the THF are deoxygenated by simply pumping their containers for 3cycles on a Schlenk line. The Ti(O^(i)Pr)₄ is placed in an air-freestorage flask and then freeze-pumped-thawed. All liquid reagents aretransferred to separate pre-heat dried, air-free flasks inside theglovebox. Stearyl alcohol is used as supplied without furtherpurification.

The entirety of Reaction No. 3 is performed on a Schlenk line underargon atmosphere. The co-solvent system of toluene and THF can heat forat time at 85° C. The co-solvents are then added to a round bottom airfree flask having LiAlH₄, where the metal hydride is dissolved in thestirring toluene and tetrahydrofuran mixture. Other ethers besidetetrahydrofuran can be used such as diethyl ether or 1,4-dioxane. Athermocouple is inserted into the reaction mixture to monitor thetemperature of the reaction.

Once the LiAlH₄ is added to the hydrocarbon-ether co-solvent system, thereaction temperature is increased from about 100° C. to about 110° C.,or the reaction mixture can remain at about 85° C. with a heating mantlewhile stirring with a stir bar. In a separate air-free flask, thetitanium isopropoxide is dissolved in toluene to create a solution witha concentration of ˜10% v/v. Once the reaction mixture reaches from 85°C. to about 110° C., the titanium isopropoxide solution is added tocatalyze the decomposition of LiAlH₄.

The decomposition reaction is left heating and stirring for ˜10 minutesuntil the stearyl alcohol is added. The stearyl alcohol is used directlyas supplied and dissolved in THF prior to addition to the reactionmixture. The concentration of the stearyl alcohol is on the 0.5-2 Mrange.

Once the stearyl alcohol is added, the reaction mixture can react for aduration from about 0.5 hours to about 2 or more hours. After about a2-hour reaction time, the solvent is removed by boiling in vacuo or canbe removed by filtration or other methods. A theoretical yield of 6 g ofnMx₁₂ is produced.

Reaction No. 4: Creating nMx₁₃

Reaction No. 4 and its corresponding data relates to our process formaking and identifying nMx₁₃. It is an aspect of the present inventionwherein nMx₁₃ is produced by a bottom up synthesis that createsnanoparticles of both Li₃AlH₆ and elemental Al metal that are carefullysized and passivated at the controlled first reaction step of LiAlH₄decomposition, where the capping agent is a long chain carboxylic(fatty) acid. It is an embodiment of the present invention wherein thecapping agent is stearic acid, where passivation is by way of aluminumoxygen bonding between the oxygen atoms available on the capping agentand the surfaces of the aluminum nanoparticle and can be stated simplyas:Core NPs+stearic acid→nMx-stearyl carboxylate+H₂(g),wherein the organic layer binds to the composite through aluminum oxygenbonds thereby forming stearyl carboxylate at the composite's aluminumsurfaces.

The following chemicals for making nMx₁₃ are purchased fromSigma-Aldrich and are as follows: Lithium aluminum hydride (LiAlH₄(95%)), titanium isopropoxide (Ti(O^(i)Pr)₄, 97%), toluene (anhydrousgrade, 99.8%), tetrahydrofuran (THF, anhydrous grade, ≥99.9%,inhibitor-free), and stearic acid.

The solvents toluene and THF are not distilled and are kept in aglovebox, since they are anhydrous. Before reaction, both the tolueneand the THF are deoxygenated by simply pumping their containers for 3cycles on a Schlenk line. The Ti(O^(i)Pr)₄ is placed in an air-freestorage flask and then freeze-pumped-thawed. All liquid reagents aretransferred to separate pre-heat dried, air-free flasks inside theglovebox. The stearic acid is placed in an air-free flask and heatedwith a heat gun under vacuum with a Schlenk line. The stearic acid ismelted and some degassing is observed. The stearic acid can return toroom temperature, in which the stearic acid solidified. The stearic acidis purged with argon gas. This cycle is done twice to further reduce thewater content.

The entirety of Reaction No. 4 is performed on a Schlenk line underargon atmosphere. The co-solvent system of toluene and THF can heat forat time at 85° C. LiAlH₄ is then added to a round bottom, air-free flaskand dissolved in the stirring toluene and tetrahydrofuran mixture. Otherethers beside tetrahydrofuran can be used such as diethyl ether or1,4-dioxane. A thermocouple is inserted into the reaction mixture tomonitor the temperature of the reaction.

Once the LiAlH₄ is added to the hydrocarbon-ether co-solvent system thereaction temperature is increased from about 100° C. to about 110° C.,or the reaction mixture can remain at about 85° C. with a heating mantlewhile stirring with a stir bar. In a separate air-free flask, thetitanium isopropoxide is dissolved in toluene to create a solution witha concentration of ˜10% v/v. Once the reaction mixture reaches from 85°C. to about 110° C., the titanium isopropoxide solution is added tocatalyze the decomposition of LiAlH₄.

The decomposition reaction is left heating and stirring for ˜10 minutesuntil the stearic acid is added. The stearic acid is used directly assupplied and dissolved in THF prior to addition to the reaction mixture.The concentration of the stearic acid is in the 0.5-2 M range.

Once the stearic acid is added, the reaction mixture can react for aduration from about 0.5 hours to about 2 or more hours. After about a 2hour reaction time, the solvent is removed by boiling in vacuo or can beremoved by filtration or other methods. The organic content of the finalnMx₁₃ is about 50% w/w. A theoretical yield of 6 g of nMx₁₃ is produced.

Reaction No. 5: Creating nMx₁₄-nMx₁₈

Reaction No. 5 is exemplary for each of nMx₁₄-nMx₁₈ and itscorresponding data relates to our process for making the same. It is anaspect of the present invention wherein these iterations of nMx areproduced individually via a bottom up synthesis that createsnanoparticles of both Li₃AlH₆ and elemental Al metal that are carefullysized and passivated at the controlled first reaction step of LiAlH₄decomposition. However, the capping agent is a combination of a fattyacid, a fatty alcohol, PEG with an alkadiene, tetraethylene glycol ortriethylene glycol (an oligomer of ethyelene glycol), or anycombinations thereof. The combinations and ratios for each of theseorganics are given in Table 6.

TABLE 6 nMx₁₄-nMx₁₈ and the ratios for capping agent combinations.octadecanol tetraethylene glycol nMx Iteration % w/cap % w/cap nMx₁₄70.1% 29.9% nMx₁₅ 58.4% 41.6% nMx₁₆ 44.3% 55.7% nMx₁₇ 35.0% 65.0% nMx₁₈23.4% 76.6%

It is an embodiment of the present invention wherein the combination ofcapping agents facilitates passivation of the composite by way ofaluminum oxygen bonding between the oxygen atoms available for eachcapping agent and the surfaces of the aluminum nanoparticle and can bestated simply as:Core NPs+fatty acid/alcohol or PEG+alkadiene→organic-O-nMx+H₂(g),wherein the organic layer binds to the composite through aluminum oxygenbonds thereby forming a complex organic oxygen interface at thecomposite's aluminum surfaces. In addition, the reaction will releaseH_(2(g)) and, in cases where the fatty alcohol or acid is unsaturated,may result in copolymerization of the complex organic layer bound viathe aluminum oxygen bonding.

The following chemicals for making nMx₁₄-nMx₁₈ are purchased fromSigma-Aldrich and are as follows: Lithium aluminum hydride (LiAlH₄(95%)), titanium isopropoxide (Ti(O^(i)Pr)₄, 97%), toluene (anhydrousgrade, 99.8%), tetrahydrofuran (THF, anhydrous grade, ≥99.9%,inhibitor-free), stearic acid, stearyl alcohol, 1, 7-octadiene, andPolyethylene glycol (PEG) (average molecular weight (MO of 6000 amu andhaving water content of ≤1% w/w).

For simplicity, the following details the method for making nMx₁₆, wherethe co-capping agents tetraethylene glycol (an oligomer of ethyeleneglycol) and stearyl alcohol are used to passivate the corenanoparticles. The solvents toluene and THF are not distilled and arekept in a glovebox, since they are anhydrous. Before reaction, both thetoluene and the THF are deoxygenated by simply pumping their containersfor 3 cycles on a Schlenk line. The Ti(O^(i)Pr)₄ is placed in anair-free storage flask and then freeze-pumped-thawed. All liquidreagents are transferred to separate pre-heat dried, air-free flasksinside the glovebox. The PEG is placed in an air-free flask and heatedwith a heat gun in vacuo on a Schlenk line. The PEG is melted and somedegassing is observed. The PEG is allowed to return to room temperatureand re-solidify. The PEG is purged with argon gas. This cycle is donetwice to further reduce the water content.

The entirety of Reaction No. 5 is performed on a Schlenk line underargon atmosphere. The co-solvent system of toluene and THF can heat forat time at 85° C. LiAlH₄ is then added to a round bottom, air-free flaskand dissolved in the stirring toluene and tetrahydrofuran mixture. Otherethers beside tetrahydrofuran can be used such as diethyl ether or1,4-dioxane. A thermocouple is inserted into the reaction mixture tomonitor the temperature of the reaction.

Once the LiAlH₄ is added to the hydrocarbon-ether co-solvent system thereaction temperature is increased from about 100° C. to about 110° C.,or the reaction mixture can remain at about 85° C. with a heating mantlewhile stirring with a stir bar. In a separate air-free flask, thetitanium isopropoxide is dissolved in toluene to create a solution witha concentration of ˜10% v/v. Once the reaction mixture reaches from 85°C. to about 110° C., the titanium isopropoxide solution is added tocatalyze the decomposition of LiAlH₄.

The decomposition reaction is left heating and stirring for ˜10 minutesuntil the combination of capping agents is added. Note that adding thecombination of capping agents according to Table 3 will form the desirediteration of nMx₁₄-nMx₁₈. The PEG is prepared by dissolving it in ˜85 mLof toluene in a separate air-free flask, and some heat is applied to thesolution to aid in dissolving the capping agent. The reaction uses 3 gof PEG to produce a 50 w/w of organic content of a 6 g yield of nMx₁₆.The PEG may consist of one number average molecular weight (M_(n)) or amixture of M_(n).

Once the combination of capping agents is added, the reaction mixture isallowed to react for a duration from about 0.5 hours to about 2 or morehours. After about a 2-hour reaction time, the solvent is removed byboiling in vacuo or can be removed by filtration or other methods. For atypical synthesis, nMx₁₆ is capped with polyethylene glycol (PEG,M_(n)=6000 amu). The organic content of the final nMx₁₆ is about 50 w/w.A theoretical yield of 6 g of nMx₁₆ is produced.

Reaction No. 6: nMx₁₉ & nMx₂₀

Reaction No. 6 and its corresponding data relates to our process formaking and identifying nMx₁₉ and nMx₂₀. It is an aspect of the presentinvention wherein both nMx₁₉ and nMx₂₀ are produced by a bottom upsynthesis that creates nanoparticles of both Li₃AlH₆ and elemental Almetal that are carefully sized and passivated at the controlled firstreaction step of LiAlH₄ decomposition, where the capping agents variousPEGs, PEO, or TEG of varying molecular weights.

For nMx₁₉, larger molecular weight PEG systems (from about 500 amu toabout 6000 amu) are used as the capping agent, where the percent oxygenby mass of the PEG cap varies from about 36.4% to about 39%. For nMx₂₀,triethylene glycol (PEG with 3 monomer units) and/or tetraethyleneglycol are used as capping agents, with 42.6% and 41.2% by mass oxygenmass of the capping agent, respectively.

It is an embodiment of the present invention wherein passivation ofeither nMx₁₉ or nMx₂₀ is by way of aluminum oxygen bonding between theoxygen atoms available on the capping agent and the surfaces of thealuminum nanoparticle and can be stated simply as:Core NPs+PEG→nMx-PEG+H₂(g),wherein the organic layer binds to the composite through aluminum oxygenbonds thereby forming an nMx-PEG complex.

The following chemicals for making nMx₁₉ and nMx₂₀ are purchased fromSigma-Aldrich and are as follows: Lithium aluminum hydride (LiAlH₄(95%)), titanium (IV) isopropoxide (Ti(O^(i)Pr)₄, 97%), toluene(anhydrous grade, 99.8%), tetrahydrofuran (THF, anhydrous grade, ≥99.9%,inhibitor-free), PEO, Polyethylene glycol (PEG) (average molecularweight (Mn) of 6000 amu and having water content of ≤1% w/w) [nMx₁₉],triethylene glycol (PEG with 3 monomer units), and tetraethylene glycol(TEG) [nMx₂₀].

The solvents toluene and THF are distilled and kept in a glovebox.Before reaction, both the toluene and the THF are deoxygenated by simplypumping their containers for 3 cycles on a Schlenk line. TheTi(O^(i)Pr)₄ is placed in an air-free storage flask and thenfreeze-pumped-thawed. All liquid reagents are transferred to separatepre-heat dried, air-free flasks inside the glovebox. The PEG is placedin an air-free flask and heated with a heat gun in vacuo on a Schlenkline. The PEG is melted and some degassing is observed. The PEG canreturn to room temperature and resolidify. The PEG is purged with argongas. This cycle is done twice to further reduce the water content.

The entirety of the reaction is performed on a Schlenk line under argonatmosphere. LiAlH₄ is introduced into a round bottom, air-free flaskwithin a glovebox. Under a Schlenk line, the co-solvent system oftoluene and THF are added to the flask containing LiAlH₄. The reactionmixture can heat for a time at 85° C. Other ethers besidetetrahydrofuran can be used such as diethyl ether or 1,4-dioxane. Athermocouple is inserted into the reaction mixture to monitor thetemperature of the reaction.

Once the LiAlH₄ is added to the hydrocarbon-ether co-solvent system thereaction temperature is increased from about 100° C. to about 110° C.,or the reaction mixture can remain at about 85° C. with a heating mantlewhile stirring with a stir bar. In a separate air-free flask, thetitanium (IV) isopropoxide is dissolved in toluene to create a solutionwith a concentration of ˜10% v/v. Once the reaction mixture reaches from85° C. to about 110° C., the titanium (IV) isopropoxide solution isadded to catalyze the decomposition of LiAlH₄.

The decomposition reaction is left heating and stirring for ˜10 minutesuntil the PEG is added. The PEG is prepared by dissolving in ˜85 mL oftoluene or THF in a separate air-free flask, and some heat is applied tothe solution to aid in dissolving the capping agent. The reaction uses 3g of PEG to produce a w/w of organic content of a 6 g yield of nMx₂₀.The PEG may consist of one number average molecular weight (M_(n)) or amixture of M_(n).

Once the PEG is added, the reaction mixture can react for a durationfrom about 0.5 hours to about 2 or more hours. After about a 2-hourreaction time, the solvent is removed by boiling in vacuo or can beremoved by filtration or other methods. For a typical synthesis, nMx₂₀is capped with tetraethylene glycol (PEG with four monomer units andMn=6000 amu). The organic content of the final nMx₂₀ is about 50% w/w toabout 55% w/w. A theoretical yield of 6 g of nMx₂₀ is produced. FornMx₁₉, the nanoscale organic layer is a blend of polyethylene glycolhaving Mn=600 amu and Mn=6000 amu, where the blend may range from 1:1 toabout 35:1.

nMx can be incorporated with a secondary high explosive by anytraditional means, including slurry casting (with an appropriate solventsuch as an ether or a hydrocarbon) of nMx and a secondary highexplosive, or by directly pressing a pellet of nMx with the secondaryhigh explosive, or by using an epoxide binder (or other appropriatebinder) to combine the nMx and the secondary high explosive into aformable composite. nMx can be included into a secondary high explosivecomposite in concentrations ranging from about 0.1% w/w up to about 50%w/w.

Powder X-Ray Diffraction—nMx Structural Analysis

Powder X-Ray Diffraction (PXRD) is an analytical technique known in theart to categorize samples having crystalline phases. With PXRD, X-rayswavelengths relative to a diffraction angle can give insight into thelattice spacing of a nanocomposite's crystalline structure. nMx isfinely ground into a powder and irradiated with X-rays to extractcharacteristic peaks from scattered waves. Only Li₃AlH₆ and elemental Alare in detectable amounts in crystal form and thus render PXRD peaks,indicating the lack of byproducts in our nanocomposite.

The PXRD scans for nMx samples are performed on a Rigaku XRD MiniFlex600 diffractometer that has a Cu source operated at 40 kV/15 mA and ascintillation counter detector. Conversion of the diffraction peaks tod-spacings allows for further identification of nMx's core metals, asgiven for nMx₁₀. In addition, a Scherrer analysis is performed todiscern the particle sizes from the peak widths of the diffractogram.The analysis uses an equation that relates the size of nanoparticles ina solid to the broadening of a peak in the diffractogram. The equationis as follows:τ=Kλ/β cos Θ,where τ is the mean size of the ordered (crystalline) domains, K is adimensionless shape factor, λ is the wavelength of the X-ray, β is linebroadening in radians, and Θ is the Bragg angle. Because the nanoscaleorganic layer is not a crystalline material, the nanocomposite'spassivation layer cannot be examined by constructive interference ofdiffracted X-rays as defined by Bragg's Law (nλ=2d sin θ), meaning thefundamental stretching frequencies of the nanoscale organic layer willbe qualified via Raman and FTIR spectroscopy.

FIGS. 4-9 depict PXRD diffractograms for nMx₁₁, nMx₁₂, nMx₁₃, nMx₁₆,nMx₁₉, and nMx₂₀ respectively. Each iteration of nMx gives, on theaverage, very similar peaks at 2Θ, where the average peak positions forFIGS. 4-9 that characterize the two distinct nanoparticles are given inTable 7 along with their corresponding Miller indices and Scherrernanoparticle sizes. The diffractograms depicted in FIGS. 4-9 show they-axis labeled as Relative Intensity from 0% to 100%. The x-axis isrendered in degrees relative to 2Θ. For all nMx PXRD scans, the Al (111)plane located at about 38.4° has the highest peak intensity. All otherpeak intensities corresponding to crystalline Al and Li₃AlH₆ aremeasured relative to the intensity of the Al (111) peak.

The average relative intensities for the other peaks corresponding tocrystalline Al nanoparticles, across the as mentioned nMx sampleselection, are as follows: the Al (200) peak at 44.7° has a relativeintensity of 49%; the Al (220) peak at 65.1° has a relative intensity of32%; the Al (311) peak at 78.2° has a relative intensity of 30%; and theAl (222) peak at 82.4° has a relative intensity of 12%.

The crystalline Al nanoparticles peaks are larger in intensity and morepronounced than the peaks belonging to Li₃AlH₆ nanoparticles. Li₃AlH₆nanoparticles have a lower scattering cross section for the X-rays dueto 90% of the atoms in Li₃AlH₆ having a low atomic weight (Li and H),which renders peak intensities that are lower in magnitude relative tothe heavier Al atomic core.

Li₃AlH₆ nanoparticles render PXRD double, or unresolved peaks, at 20.The average relative intensities for the peaks corresponding tocrystalline Li₃AlH₆ nanoparticles, across the as mentioned nMx sampleselection, are as follows: Li₃AlH₆ (110) peak at 21.9° has a relativeintensity of 29%; Li₃AlH₆ (012) peak at 22.5° has a relative intensityof 30%; Li₃AlH₆ (202) peak at 31.7° has a relative intensity of 16%.

The average Scherrer width of the Al (111) peak at 38.4° relative to 2Θfor the various types of nMx is 18 nm. The average Scherrer width of theLi₃AlH₆ (202) peak at 37.1° relative to 2Θ for the various types of nMxis 23 nm. PXRD scans confirm that our method produces elemental Alnanoparticles and Li₃AlH₆ nanoparticles that are below 50 nm. Therefore,it is an aspect of the present invention wherein the lower limit ofnMx's nanoparticle size distribution for elemental Al core metals isabout 18 nm and the lower limit for nanoparticle size distribution forLi₃AlH₆ core metals is about 23 nm.

TABLE 7 PXRD data for various nMx iterations at 2θ, Relative Intensity,Lattice spacing, and Scherrer size. Core Metal NPs Li₃ALH₆NPs ElementalAl NPs 2θ Diffraction 21.9° 22.5° 31.7° 38.4° 44.7° 65.1° 78.2° 82.4°Relative 29% 30% 16% 100% 49% 32% 30% 12% Intensity Lattice spacing(110) (012) (202) (111) (200) (220) (311) (222) NPs Scherrer 23 nm 18 nmSize

FTIR & Raman Data—nMx Spectroscopic Analysis

Because the nanoscale organic layer is not a crystalline material, thepassivation agent for the core nanoparticles cannot be examined byconstructive interference of diffracted X-rays as defined by Bragg's Law(nλ=2d sin θ). nMx's nanoscale organic layer is analyszed viatraditional FTIR and Raman spectroscopy, which are well known in theart. Raman spectroscopy measures scattered laser light based on thefundamental stretching frequencies of the nanoscale organic layer toobserve vibrational, rotational, and other low-frequency modes inorganics, giving a finger print for each passivation agent about thecore nanopartilces.

FIG. 10 depicts FTIR stretching frequencies of the nanoscale organiclayer for nMx₂₀. The nanoscale organic layer is a glycol and shows aband at 1080 cm⁻¹ (C—O stretching in the glycol) and at 2850-2970 cm⁻¹(C—H stretching in the glycol). This indicates that the there is anassociation with the glycol nanoscale organic layer and the two distinctcore nanoparticles.

FIG. 11-FIG. 14 are Raman spectra for nMx₁₂, nMx₁₃, nMx₁₆, and nMx₁₉repsectively. FIG. 11 depicts Raman scattering for nMx₁₂, where the scanis performed from 500 cm⁻¹ to 3500 cm⁻¹ for octadecanol as the nanoscaleorganic layer. Octadecanol gave Raman frequencies for nMx₁₂ at about1092 cm⁻¹ (C—O stretch) and at about 2850-2920 cm⁻¹ (C—H stretch).

FIG. 12 depicts Raman scattering for nMx₁₃, where the scan is performedfrom 500 cm⁻¹ to 3500 cm⁻¹ for octadecanoic acid as the nanoscaleorganic layer. Octadecanoic acid gave Raman frequencies for nMx₁₃ atabout 1294 cm⁻¹ (C—O stretch), at about 1645 cm⁻¹ (C═O stretch), and atabout 2841-3024 cm⁻¹ (C—H stretch).

FIG. 13 depicts Raman scattering for nMx₁₆, where the scan is performedfrom 500 cm⁻¹ to 3500 cm⁻¹ for a mixture of octadecanol and TEG as thenanoscale organic layer. The mixture of octadecanol and TEG gave Ramanfrequencies for nMx₁₆ from about 2839 cm⁻¹ to about 2915 cm⁻¹ (C—Hstretch). Note that the C—O stretch is too weak and not observable.

FIG. 14 depicts Raman scattering for nMx₁₉, where the scan is performedfrom 500 cm⁻¹ to 3500 cm⁻¹ for PEG as the nanoscale organic layer. PEGgave Raman frequencies for nMx₁₉ at about 1086 cm⁻¹ (C—O stretch) and atabout 2868-2950 cm⁻¹ (C—H stretch).

It is an aspect of the present invention wherein nMx₁₁ through nMx₂₀ maybe identified as a nanometallic organic hybrid that is best described bythe combination of PXRD peaks for both core nanoparticles and the Ramanfundamental strecthing frequencies of the agents used for the nanoscaleorganic layer as follows: L₁₃AlH₆ nanoparticles giving PXRD double peaksat 2Θ at about about 21.9°, at about 22.5°, and at about 31.7°,elemental Al nanoparticles giving PXRD peaks at 2Θ at about 38.4°[highest peak], about 44.7°, at about 65.1°, at about 78.2°, and about82.4°, and the nanoscale organic layer giving C—O stretching frequenciesfrom about 1086 cm-1 to about 1294 cm⁻¹, C═O stretching frequencies ofabout 1645 cm⁻¹, C—H stretching frequencies from about 2841 cm⁻¹ toabout 3024 cm⁻¹.

DSC/TGA—nMx Thermal Analysis

Because nMx can be used as an advanced fuel in various applications,DSC/TGA data examines the thermal behavior of the present invention.Differential Scanning calorimetry/Thermo Gravimetric Analysis (DSC-TGA)are combined thermal analysis techniques that find combustion events ofa sample relative to time and increased heat (DSC) and mass change of asubstance relative to the same (TGA). The DSC-TGA analysis is done on TAInstruments DSC/TGA SDT Q600. The exotherms for various nMx iterationsgive ignition and combustion events for the Li3AlH6 nanoparticles, theelemental Al nanoparticles, and the nanoscale organic layer in air. TheDSC scanning rate for all nMx scans are either 5° C. per minute (nMx₁₂),10° C. per minute (nMx_(10, 11, 16, 19, and 20)), or ˜20° C. per minute(nMx₁₃).

FIG. 15 depicts DSC-TGA curves for nMx₁₀ and commercial Li₃AlH₆ underambient air flow. The nanoscale organic layer is octadiene for nMx₁₀.The DSC-TGA scan of nMx₁₀ is compared with the DSC-TGA scan ofcommercial Li₃AlH₆. The DSC onset temperature of the exotherm on nMx₁₀is at 252° C., which is like the onset of the exotherm (218° C.) locatedon the commercial Li₃AlH₆. The slight bump at 600° C. is attributed tothe ignition and combustion of elemental Al nanoparticles. The TGA showsmass gains for these exotherms on the nMx₁₀ and commercial Li₃AlH₆ aredue to the combustion with oxygen gas to produce the solid combustionproducts of Li₂O and Al₂O₃.

FIG. 16 displays DSC-TGA curves for nMx₁₁ under ambient air flow withepoxydecene and an alkadiene as the nanoscale organic layer. Thestarting materials for nMx₁₁ are mixed at ratios of 10:1:2 ofLiAlH₄:epoxydecene:octadiene respectively, and where the nanoscaleorganic layer is a mixture of epoxydecene and octadiene. The DSCexotherm for nMx₁₁, being the solid black line, exhibits an Li₃AlH₆exotherm with an onset of 160° C. nMx₁₁ also exhibits an exothermrelated to elemental Al nanoparticle combustion, in which the onset isat 586° C. Also note that there is a small exothermic peak at about 380°C. This peak can be attributed to the combustion of the nanoscaleorganic layer. We believe the decrease from 450° C. onward is due toother chemical species such as Li₂O and Al₂O₃ and the like.

FIG. 17 displays DSC-TGA curves for nMx₁₂ under ambient air flow with50% steryl-alcohol as the nanoscale organic layer. For nMx₁₂, twoexothermic peaks correspond to the combustion of Li₃AlH₆. The firstexothermic peak is accompanied with a mass gain and its onset is at 110°C., in which the mass gain is due to the association with molecularoxygen during the combustion of Li₃AlH₆. The second exothermic peak isaccompanied with a mass loss and its onset is at 265° C. This mass lossis due to the combustion of the organic cap into gaseous combustionproducts, which is offset with the mass gain of the oxidation ofLi₃AlH₆. Another exotherm related to the combustion of the Alnanoparticles occur with an onset of 568° C. In addition, anotherexotherm is observed with an onset of 690° C., which is related to thereaction of Li₂O and Al₂O₃ associates together to produce LiAlO₂.

FIG. 18 displays DSC-TGA curves for nMx₁₃ under ambient air flow with44% oleic acid as the nanoscale organic layer. nMx₁₃ has a similarDSC-TGA profile as nMx₁₂. It also exhibits two exotherms related to thecombustion of Li₃AlH₆ at 90° C. and 270° C., in which the first exothermexperiences a mass gain and the second exotherm experiences a mass loss.The intense peak at about 325° C. is attributed to the ignition andcombustion of the nanoscale organic layer. It also has two exothermsrelated to the combustion of Al and the appearance of LiAlO₂ at therespective onset temperatures of 570° C. and 700° C.

FIG. 19 displays DSC-TGA curves for nMx₁₆ under ambient air flow with amixture of octadecanol/TEG as the nanoscale organic layer. nMx₁₆ has asimilar DSC-TGA profile with nMx_(12/13). The exotherm onsets of Li₃AlH₆are at 125° C. and 270° C. The onsets of exotherms of elemental Alnanoparticle combustion and LiAlO₂ association are located respectivelyat 560° C. and 670° C.

FIG. 20 displays DSC-TGA curves for nMx₁₉ under ambient air flow withPEG 600 as the nanoscale organic layer. nMx₁₉ gives three exotherms witha mass loss that are related to the combustion of Li₃AlH₆, in which theonsets are located at 110° C., 250° C., and 430° C. Three exothermicpeaks due to the combustion of Li₃AlH₆ rather than two peaks like thenMx12/13/16 may occur since there is a trimodal size distribution ofLi₃AlH₆ nanoparticles in nMx₁₉. The exothermic onset for elemental Alnanoparticle combustion is at 550° C., and the exothermic onset ofLiAlO₂ association is located at 675° C. The relative amount ofexothermic heat (integral of peak) relating to production of LiAlO₂ ismuch larger than the same peak in the formulations of nMx₁₀₋₁₆ possiblybecause the diol of a PEG molecule covalently links an Al and Li₃AlH₆nanoparticle, which reduces their interfacial distance.

Although DSC-TGA scans for nMx₂₀ are not shown, the scans disclose fiveexothermic peaks related to the Li₃AlH₆ nanoparticles located with anonset of 90° C., 200° C., 280° C., 340° C., 470° C. The modes of sizedistribution have increased with nMx₂₀ over the nMx₁₉ perhaps due to thesmaller size of the tetraethylene glycol over the PEG molecules, inwhich smaller molecules may provide a greater number of sizedistributions. The exothermic peak for elemental Al nanoparticlecombustion has an onset of 525° C. Like nMx₁₉, a relatively large amountof exothermic heat is produced from the association of LiAlO₂, in whichthe onset is at 665° C.

In total, the DSC data shows that a few exotherms are located at about200° C.-400° C., which are due to the combustion of Li₃AlH₆nanoparticles with oxygen to produce Li₂O and Al₂O₃ and the unexpectedcombustion event of the nanoscale organic layer immediately after thesame. Another important exotherm is located at about 600° C., which isdue to the combustion of elemental Al nanoparticles to produce Al₂O₃. Inaddition, an exotherm at about 700° C. is due to the reaction betweenthe Li₂O and Al₂O₃ to produce lithium aluminate, LiAlO₂. The TGA datainfers that the exotherms are accompanied by either a mass gain due tothe oxidation of the metals or a mass loss due to the capping agentoxidation to produce combustion gases.

DSC data indicates that nMx, on average, can render at least threecombustion events. Two combustion events can be attributed to the corenanoparticles and another to the combustion of the nanoscale organiclayer. nMx and certain oxidizers used in combustion processes ignitewithin the same temperature ranges. If the oxidizer, a nonlimitingexample being ammonium perchlorate, and the nMx nanocomposite ignitewithin the same temperature range, then the multiple combustion behaviorcould lead to improved advanced fuels or additives that give a uniqueburning behavior for many combustion applications.

TEM Data—nMx Nanoparticle Images

True nanoparticles for nMx are readily seen in TEM images shown in FIGS.21-26. Transmission Electron Microscopy (TEM) is a well-knownspectroscopic technique for giving high resolution images of samplesthat are 100 nm or less in diameter. All images were taken using a JEOL1200ex TEM operated at 60 kV. Samples were cast on formvar TEM grids. Animage analysis software suite, non-limiting examples being MacTempasimage simulation software, Cerius2, EMAN, IMAGIC, CCP4, CRISP, MRC, orFEI Amira, was used to properly analyze nanoparticle size distributionsfor nMx samples.

With TEM, an image is formed from the interaction of electrons with thesample as the beam is transmitted through the specimen. This imageprovides information about the space group symmetries and orientation ofthe single crystal nanoparticles relative to the electron beam's path,giving the physical dimensions of the nanoparticles or a nanoscale sizedistribution of the same [22]. While PXRD scans identify the nanoscaleextent of the crystalline domains, true nanoparticle nature is confirmedby TEM imaging.

TEM images show that the shape and size of nMx nanoparticles varydepending on the type of passivation agent used during the reaction andthe push and pull of reaction conditions. FIG. 21 depicts two separateTEM images of nMx₁₀, where core metal nanosurfaces are passivated byoctadiene as the nanoscale organic layer. FIG. 21 shows the heavier massof the core metals appearing as dark spots, being elemental Al andLi₃AlH₆ nanoparticles, surrounded by the lower density of the nanoscaleorganic layer, as shown by the lower contrast. The average nanoparticlesize is 50 nm.

FIG. 22 depicts TEM imaging of nMx₁₂, where core metal surfaces arepassivated by 50% steryl alcohol as the nanoscale organic layer. FIG. 22shows the core metals as dark rods having a 1-dimensional (nanowire)shape for both elemental Al and Li₃AlH₆ nanoparticles. The lower densityof the nanoscale organic layer surrounds the rods as a passivatingagent, as shown by the lower contrast. The average nanoparticle size is100 nm.

FIG. 23 depicts TEM imaging of nMx₁₃, where the surfaces of the corenanoparticles are passivated by 44% oleic acid as the nanoscale organiclayer. FIG. 23 shows the heavier mass of the core metals appearing asdark spots, being elemental Al and Li₃AlH₆ nanoparticles, surrounded bythe lower density of the nanoscale organic layer, as shown by the lowercontrast. The average nanoparticle size is 50 nm.

FIG. 24 depicts TEM imaging nMx₁₆, where core metal nanosurfaces arepassivated by a mixture of octadecanol/TEG as the nanoscale organiclayer. FIG. 24 shows the core metals as dark rods having a 1-dimensional(nanowire) shape for both elemental Al and Li₃AlH₆ nanoparticles. Thelower density of the (lower contrast) nanoscale organic layer surroundsthe rods as a passivating agent, as shown by the lower contrast. Theaverage nanoparticle size is 100 nm.

FIG. 25 depicts TEM imaging for nMx₁₉, where core metal nanosurfaces arepassivated by PEG 600 as the nanoscale organic layer. FIG. 25 shows theheavier mass of the core metals appearing as dark spots, being elementalAl and Li₃AlH₆ nanoparticles, surrounded by the lower density of thenanoscale organic layer, as shown by the lower contrast. The averagenanoparticle size is 100 nm.

FIG. 26 depicts TEM imaging for nMx₂₀, where core metal nanosurfaces arepassivated by TEG as the nanoscale organic layer. FIG. 26 shows theheavier mass of the core metals appearing as dark spots, being elementalAl and Li₃AlH₆ nanoparticles, surrounded by the lower density of thenanoscale organic layer, as shown by the lower contrast. The averagenanoparticle size is 100 nm.

nMx Heats of Formation

From Table 8, nMx composites have very high combustion enthalpies (inthe range of −24 kJ/g to −38 kJ/g), significantly exceeding that ofother aluminum-containing nanomaterials which typically have maximumtheoretical combustion enthalpies of −30.9 kJ/g. All nMx materials havevery high burn rates in oxygen. The gravimetric heat of combustion fornMx materials varies from ˜−28 kJ/g (nMx₂₀) to −39 kJ/g (nMx₁₂).Metallized combustibles are typically in the range of from about −25kJ/g to about −31 kJ/g.

TABLE 8 Measured & Theoretical ΔH° values for the family of nMxnanocomposites. Measured Theoretical nMx Iteration ΔH° ΔH° NanoscaleOrganic Layer nMx₁₁ −24 kJ/g −40 kJ/g epoxydecene + alkadiene nMx₁₂ −38kJ/g −39 kJ/g octadecanol nMx₁₃ −35 kJ/g −37 kJ/g oleic acid nMx₁₆ −29kJ/g −34 kJ/g Octadecanol/tetraethylene glycol nMx₁₉ −27 kJ/g −31 kJ/gPEG (Mn = 6000 (55% by weight of PEG mixture) and 600 (20% by weight ofPEG mixture) nMx₂₀ −28 kJ/g −30 kJ/g Tetraethylene glycol

nMx and its various uses as an explosive enhancer and a solid fuel grainfor rocket motors are further discussed below.

nMx as Explosive Enhancer

Either nMx₁₉ or nMx₂₀ can be associated with a secondary high explosiveby traditional means to enhance shockwave velocity and explosivepressure. Because the enhancer acts as both fuel and oxidizer, thenanocomposite combusts to release self-sustained heat energy thatincreases the propagation speed of a shockwave through a chemicalexplosive and raises the temperature (Q) and pressure (V) of newlyformed hot gases by the same, thereby creating a more effective blast,where Explosive power=Q×V. Although there is a specific mention fornMx₁₉ and nMx₂₀ to act as explosive enhanceers, it is an embodiment ofthe present invention for nMx₁₂₋₁₈ to also be asssociated with asecondary high exlosive by traditional means to enhance shockwavevelocity, where these materials can possibly contribute more totalenergy over a longer period of time to the shock wave enhancement.

An explosion is a result of rapid combustion and is characterized by:the decomposition or rearrangement of chemicals by heat or byshockwaves; self-sustaining behavior; a large release of heat; and theformation of hot gases that increase localized pressure and expandsurrounding air molecules to create a blast wave and shock front [25].When a chemical explosive is detonated, hot gases produced duringdetonation expand and facilitate the propagation of a shockwave throughthe surrounding medium that affects the air molecules about the blast[25].

The enhanced explosive may be made via slurry casting either nMx₁₉ ornMx₂₀ with a secondary high explosive in an appropriate solvent, such asan ether or a hydrocarbon. The enhanced explosive may also be made bydirectly pressing a pellet of the enhancer with a secondary highexplosive or by using an epoxide binder (or another appropriate binder)to combine the same. Either enhancer can be included into the secondaryhigh explosive in concentrations ranges from about 0.1% up to about 50%by weight.

It is a preferred embodiment of the present invention where the enhanceris admixed with at least one secondary high explosive including but notlimited to: 5-nitro triazol-3-one (NTO), 2,4,6-trinitrotoluene (TNT),1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), trinitro triamino benzene(TATB), 3,5-dinitro-2,6-bis-picrylamino pyridine (PYX), nitroglycerine(NG), ethylene glycol dinitrate (EGDN), ethylenedinitramine (EDNA),diethylene glycol dinitrate (DEGDN), Semtex, Pentolite, trimethylolethyl trinitrate (TMETN), tetryl,hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), pentaerythritoltetranitrate (PETN) and 2,2,2-trinitroethyl-4,4,4-trinitrobutyrate(TNETB), methylamine nitrate, nitrocellulose,N3,N3,N′3,N′3,N7,N7,N′7,N′7-octafluoro-1,5-dinitro-1,5diazocane-3,3,7,7-tetraamine (HNFX), CL-20 (HNIW)Hexanitrohexaazaisowurtzitane, nitroguanidine, hexanitrostilbene,2,2-dinitroethene-1,1-diamin (FOX-7), dinitrourea, and picric acid. Invarious aspects, the energetic material is selected from the groupconsisting of 2,4,6-trinitrotoluene (TNT),1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), AFX 757, or anycombinations thereof.

Pellet Pressing of Enhanced Secondary High Explosive

For pellet pressing, the non-limiting example follows. An 8:1 ratio of amixture of a dry secondary explosive is admixed with either nMx₁₉ ornMx₂₀ in a container. However, the concentration of either enhancer withthe secondary high explosive can be from about 0.5%/wt to about 90%/wtof the total dry mixture. Gently agitate the two ingredients until thereis a uniformed distribution of all ingredients in the mixture.

After which, a binder may be added to the uniformed mixture. It is apreferred embodiment of the present invention wherein the binder isPolyethylene glycol (PEG) and is added to the mixture in an amount thatmakes up roughly 0.5%/wt to 20%/wt of the total mixture of the twoingredients. It is an embodiment of the present invention where thebinder may include without limitation waxes, PVP, PEG 1500,hydroxypropylmethylcellulose, methylcellulose, cellulose acetate,cellulose ethers, ethylene vinyl acetate, polystyrene plastic,nitrocellulose, polyurethane rubber, hydroxyl-terminated polybutadienerubber, Viton fluoropolymer elastomeror, bis 2,2-dinitropropyl acetate[BDNPA], bis 2,2-dinitropropyl formal [BDNPA/f], or any combinations,copolymers, or varying molecular weights thereof.

After adding the binder, the total blend is placed in a mold having adesired shape for the resulting enhanced explosive. The blend iscompressed in the mold to cure the mixture, where dwell times are veryshort, being from about a few seconds up to about 5 minutes. Pelletpresses are machines that are readily known and used within the arts andare capable of compression forces that range of from about 2,000 toabout 40,000 pounds per square inch gauge to cure and shape explosivemixtures, pharmaceuticals, or any differing dry materials that need tobe blended and shaped into a uniformed composite. Use of the enhancedexplosive, meaning further processing or detonation, is not dependent oncuring time.

Also note that, the dry admixture, being the enhancer, secondary highexplosive, and the optional binder, may be subjected to an extruder,where the dry mixture is mixed using an auger or Archimedes screw,placed in a hopper, and subjected to pressure for pellet pressing. nMxcomposites may also be admixed with pyrotechnics. In contrast tosecondary high explosives, a pyrotechnic is a combustible material thatproduces a special effect when burned, e.g. fireworks. This class ofadvanced fuel produces heat, light, smoke and sound. The fuels aretypically metals including aluminum, chromium, magnesium, manganese, andthe like. Oxidizers include chlorates, chromates, nitrates, oxides andperchlorates. Binders may include waxes, manmade vinyls, a variety ofpolymers, and the like. The addition of nMx to pyrotechnics enahnces thephysical properties of the same.

Slurry Casting of Enhanced Secondary High Explosives

The enhanced secondary high explosive can also be made via slurrycasting. Here, a dispersion is created by placing either nMx₁₉ or nMx₂₀,a secondary high explosive, and a binder into a solvent bath. Thesolvent of the present invention may include, without limitation, ethylether, trichloroethane, trichlorofloromethane, benzene, toluene, xylene,naphthalene, THF, or any combinations thereof.

The dispersion is gently mixed for a time and solvent evaporated, wherethe resulting dry composite has all ingredients from the originaldispersion. The dried composite may optionally be subjected to the samemolding or casting process as described above for pellet pressing thesame or used as is for explosive applications.

FIG. 27a and FIG. 27b display a relative comparison of shockwavevelocities of secondary high explosive PETN with and without nMx₂₀[standard]. This data is generated from roughly 3 g pellets for each ofthe enhanced and standard explosive. Each pellet is initiated with RP-2detonators in a Tunnel for High-speed Optical Research (THOR). Thetesting in THOR includes at least two pellets of each mixture ratio andthe pure explosive material. The shock wave tests include Schlieren orshadowgraph high-speed imaging to record shock wave motion and determineshock speed for each pellet.

Schlieren photography is a technique well known in the arts to captureimages of showing the flow of fluids via the changes in the air thatexperiences the same. Pressure gages in THOR will record time-resolvedpressure and provide a secondary measurement of shock wave speed. TheSchlieren imaging equipment was set at 80K Frames/sec for each of FIGS.27a and 27b . FIG. 27a [right] displays shockwave propagation through anenhanced admixture of nMx₂₀ and the explosive PETN. FIG. 27b [left]displays a shockwave propagating only through explosive PETN. Theenhanced explosive of FIG. 27a gives an increased shock velocityrelative to the PETN of FIG. 27 b.

Additional Methods for Making the nMx Enhanced Explosive

It is an embodiment of the present invention for the enhanced secondaryexplosive to be manufactured via 3D printing. Any of the aboveingredients, primarily nMx₁₂₋₂₀, and the secondary high explosive, maybe associated with UV curable photopolymers such as, without limitation,acrylates, monomers, oligomers, bismaleimides, thermosetting epoxies,urethanes, polyesters, silicones, and their combinations and blends.

A typical method for making a UV curable enhanced secondary explosivewith nMx includes admixing the nanocomposite and the explosive, asdetailed above in either the pellet pressing or the slurry castingmethods, with a photopolymer resin in its near liquid or fluid state foruse in stereolithography (SLA) or Digital Light Processing (DLP)technology. SLA uses a laser to trace out the cross-sections of themodel, being 3D print instructions for a construct. Each layer isdeposited in a continuous stream of a base UV curable resin. The laseressentially “draws” the layer to be cured at UV frequencies. With DLP, aUV projector sits beneath a photopolymer reservoir and selects imagelayer for which to cure, which is ideal for 2D imaging.

Additive manufacturing of the enhanced secondary high explosive mayinclude, without limitation, the nMx enhanced explosive being added to aliquid photopolymer resin and agitated from about 0.5 hours to about 24hours at room temperature with a magnetic stirrer to ensure uniformdistribution of the enhanced explosive throughout the photopolymer'svolume. The mixture may then be loaded into an SLA 3D printer. Under UVlight, the photopolymer may solidify through a photopolymerizationreaction to form the desired 3D object defined by computer instructionscreating a construct that has a structure and weight having the nMxenhanced explosive within the UV cured matrix.

The UV cured materials, having the nMx enhanced explosive, are suitedfor making parts integral to bomb casings. Bomb casings are frequentlymade of metal or metal-alloy complexes, plastics (thermoplastic orthermoset), UV-curable materials, and adhesive resins (single ormulti-ingredient). These casings react as they are projected away fromthe reaction epicenter, releasing their energy at a certain radius orstimuli away from the epicenter. One such method would involve mixingnMx within a workable material (plastic or resin) prior to allowing thematerial to set or cure. The material casing would then harden withenergy-laden nMx encased within. A detonation, shock wave, or combustionfront would then release the energy in application from the bomb casing.

Another method for making an nMx enhanced explosive includesResonantAcoustic® Mixing. Low frequency, high-intensity, acoustic energyis used to create a uniform shear field throughout the entire mixingvessel. The result is rapid fluidization (like a fluidized bed) anddispersion of material. ResonantAcoustic® Mixing introduces acousticenergy into liquids, slurries, powders and pastes. An oscillatingmechanical driver creates motion in a mechanical system comprised ofengineered plates, eccentric weights, and springs. This energy is thenacoustically transferred to the material to be mixed. The underlyingtechnology principle is that the system operates at resonance. In thismode, there is a nearly complete exchange of energy between the masselements and the spring elements in the mechanical system that wouldensure a truly uniformed mix for the nMx and the secondary highexplosive.

nMx as a Cast or 3D printed Solid Fuel Grain

It is an embodiment of the present invention to include nMx into solidpropellant formulations, i.e. solid fuel grains for solid rocket motors(SRMs), hybrid rocket motors (HRMs), or solid fuel missiles. Morespecifically, solid formulations for SRM fuel grains may include withoutlimitation: at least one nMx nanocomposite, as detailed above, beingpressed, cast, or 3D printed with a powdered oxidizer, a polymericbinder or thermoplastic matrix, a plasticizer, a metal fuel, a curingagent, a cure catalyst, ballistic catalysts, burn rate catalysts ormodifiers, or an oil or wax into a composite shape and placed into amotor.

HRM fuel grains may include without limitation: at least one nMxnanocomposite, as detailed above, being pressed, cast, or 3D printedwith a polymeric binder or thermoplastic matrix, a plasticizer, a metalfuel, a curing agent, a cure catalyst, ballistic catalysts, burn ratecatalysts or modifiers, or an oil or wax into a composite shape andplaced into a motor, where the fuel grain is housed within or near thecombustion chamber or motor casing of an HRM. A gaseous oxidizer isstored separately from the solid fuel grain. The oxidizing gas isinjected over certain port surfaces of the fuel grain to start oxidationand combustion of the same. Hot gases form about the surfaces of thefuel gain and are expelled through a nozzle to create thrust.

Solid propellants power many missiles and rockets for military,commercial, and space applications. Solid grains for either an SRM orHRM should combust and release heat energy ata slower rate thanexplosives. nMx is an ideal material for a fuel grain as it burnsquickly while producing viable heat and a rapid gas release, less theeffect of a true explosion.

The design and functionality of a rocket motor depends on the fuelgrain's burn rate when balanced against the weight, size, and shape ofthe fuel grain, the size and shape of the combustion chamber, nozzlecharacteristics, and evolving chamber pressure to ensure that an engineachieves the necessary thrust for propulsion while being more efficientat gaining altitude, distance, and velocity. Methods to improve the burnrate of a solid fuel grain includes adding burn rate modifiers to aformulation, changing the texture of the fuel grain surfaces, alteringthe central port configuration or the fuel grain design, or modifyingthe fuel grain with various other additives.

The burn rate reflects consumption of a fuel grain relative to itsburning surface area perpendicular to the flame front within acombustion chamber. The linear burn rate of a material may be defined bythe following equation:r=[a]P _(c) ^(n),where r=linear burning rate (in/sec), a=burn rate coefficient (in/sec),P_(c)=chamber pressure (psi), and n=pressure exponent (dimensionless).The burn rate is heavily affected by the chamber pressure and temperatueabout the fuel grain's surface. A solid propellant benefits from havinga fast-linear burn rate. Rapid burning changes the mass of the objectexperiencing the thrust and forms combustion products that quickly pushthe object in the opposite direction. Due to nMx's unique burn profilehaving a low temperature ignition from about 180° C. to about 210° C.for Li₃AlH₆ nanoparticles, a combustion event for the nanoscale organiclayer at about 300° C., and the elemental Al nanoparticle combustion atabout 600° C., we believe that nMx may be tuned to produce acorresponding change in either the burn rate coefficient [a] and/orpressure exponent [n].

Increased pressure within the combustion chamber is a direct result ofthe propellants burn rate, where the flame front is perpendicular to thepropellant's surface. The formation of product gases is equal to thepropellant's burn rate by the mass flow rate equation:{dot over (m)} _(g) =A _(b)ρ_(p) r,where A_(b) is the area of the solid propellant, ρ_(p) is propellantdensity, and r is the burn rate. It is these gases, {dot over (m)}_(g),that contribute to the pressure development and the resultant thrust.

Another important measure related to the propellant's burn rate isspecific impulse, as defined by equation:F=Δm/Δt*Δυ.

The specific impulse is a measure of efficiency for combustion enginesderived from Newton's second law of motion. It is a relationship betweenthe amount of thrust produced relative to the rate in which thepropellant mass changes via the creation and expulsion rate ofcombustion gases. Because fuel expels hot gases at a mass flow rate ofΔm/Δt, F is the thrust on an object, which renders a change in velocity,Δυ, of the rocket. The force, being specific impulse or thrust, can beinterpreted as FΔt as normalized by mass.

A higher specific impulse, typically around 250 seconds or so for largerSRM and HRM motors, uses the propellant's decreasing mass to createbetter thrust, where one would want a tradeoff between a less heavypropellant or the use of less fuel for improving Δυ. Therefore, there isa need for the present invention, nMx, as a fuel additive having a largeenergy density due to nanoscale effects, that improves the efficiency ofsolid propellants for SRMs or HRMs.

Casting an nMx Solid Fuel Grain

The inclusion of nMx in fuel grains gives comparable burn rates,increased energy density, reduced HCl emissions, an overall increase infuel efficiency (thrust/mass flux), and exhibits a decrease in ignitiontemperature by circumventing the combustion inefficiency of traditionalmetal-oxide (e.g. alumina-coated) fuel additives. It is ideal for solidfuel grains to have a high specific impulse, where a fuel/oxidizer burnsfast and expels a lot of energy in a short amount of time.

The ability to add nMx to fuel grains is due to the nanoparticles beingair stable but still retaining their high energy densities andreactivity. Stated simply, being air stable makes nMx safe to handle inair long enough to press, cast, or 3D print a solid fuel formulationwhile retaining the nanoparticle's high energy densities. The fuel grainmay either be a hybrid fuel grain, where the solid fuel is made to meeta flow of a gaseous oxidizer, or a solid fuel grain, where the fuel andthe oxidizer are pressed, cast, or 3D printed into a shape within acommon composite.

One embodiment of the present invention includes the fuel grain beingformulated and mixed via methods known in the art for casting solid fuelgrains, save for the novel addition of at least one nMx nanocomposite aslisted above. A non-limiting example for making a solid fuel grain foran SRM may include placing a thermosetting binder, plasticizer, optionalburn rate catalyst, and at least one nMx composite into a mixer toblend. Note that the thermosetting binder in raw form is a liquidprepolymer or monomer, and, as such, needs the addition of a curingagent to hold the fixed shape.

A high shear mixer, or an extruder, or alternatively a simple press maybe used to mix the formulation. After which an inorganic oxidizer isadded incrementally into the active mixer until uniformity is achieved.The curing agents, cross-linking agents, or other additives may be addednow and thoroughly blended with the mix before casting into a suitablemold or rocket motor for an SRM. If desired, the mixing and casting ofthe fuel grain may be performed under vacuum to avoid air entrapmentleading to voids in the enhanced propellant.

Depending on the selected binder, the temperature of the mix may bemaintained from about 80° F. to about 175° F. to maintain a satisfactoryviscosity during mixing and casting procedures, but the temperatureshould be sufficiently low as not to ignite the nMx additive or damagethe integrity of the thermosetting binder. This procedure may befollowed to create an HRM fuel grain less the addition of the inorganicoxidizer. An HRM has the oxidizer in gaseous form and is held in aseparate tank to flow over the port surfaces of the solid grain to startoxidation and combustion of the same.

The semi-fluid formulation may be cast into a motor casing. Acylindrical type casing can be made prior to casting. It is anembodiment of the present invention where the fuel grain may be cast,molded, extruded, or in some instances machined into a cylindricallyshape having a center port that is star shaped, a circular shaped,Maltese cross shaped, clover shaped, helix shaped, double anchor, rod intube, and the like, so long as there is an outer cylindrical body havingtwo distal ends and a hollow inner cavity, or port, with a shape that isdesigned to maximize the burn rate characteristics of an SRM or HRMsolid fuel grain. It is known within the art that the quality of afinished solid fuel grain depends on the exclusion of entrapped air andupon the absence of cracks in the fuel grain's surface. We take intoconsideration that there is no extra surface area about the fuel grainto permit air pockets that would crack the solid fuel grain duringcombustion.

More specifically, it is an embodiment of the present invention forcreating a solid fuel grain wherein nMx, is lightly ground into a finepowder with a mortar and pestle and sieved to size for enhanced surfacearea and uniformity within the solid propellant. A powdered oxidizer,nonlimiting examples being bimodal ammonium perchlorate (200 & 90micron) or potassium perchlorate, is prepared by holding under vacuumfor 48 hours to dry, or alternatively, the oxidizer is omitted and willbe introduced during combustion as a gas for use in an HRM. Note thatWoodson et al. cast a fuel grain made from Li₃AlH₆ and poly-DCPD (romppolymer) that exhibited some amount of burning [26].

143 L MDI curing agent is then added to the bowl and the mixture canstir and cure for up to 45 minutes. Based on the reactivity of nMx withHTPB, it was found that allowing the propellant mixture to cure prior toaddition of the nMx results in attenuated reactivity between species andsubsequent grain growth. It is noted that if solid ingredients are addedtoo late, an inhomogeneous mixture is created and a propellant grainwith voids and delaminations is produced.

The fuel, 32-micron aluminum, is added followed by bimodal ammoniumperchlorate (200 & 90 micron in a ratio of 2:1 by mass). Before additionto the mixture, ammonium perchlorate, is dried under vacuum for about 48hours. nMx powder is then taken from an inert environment and addedimmediately after the oxidizer, where nMx is included in the cast fromabout 0.05% to about 50%, a binder being cast with a mass from about 1%to about 20%, and a solid oxidizer being cast with a mass from about 50%to about 80%.

After mixing the ingredients for 5 minutes, the formulation is heldunder vacuum for 5 minutes to remove voids and improve fuel graindensity. Grains are then cast and packed into motors, and the motors areheld under compression with a center-perf mandrel to maximize densityand minimize growth. Curing and finished fuel grains are held underinert atmosphere prior to firing. The mandrel is removed, or if nomandrel is used during casting, a lathe is used to bore out the centerof the fuel grains, and grains are weighed to allow for performanceanalysis post-firing.

Additional ingredients for making a solid fuel grain may include,without limitation, optional catalysts and additional plasticizers ormodifiers. nMx particles are defined above. The binding agent may be,without limitation, a thermosetting polymer such as hydroxyl-terminatedpolybutadiene, or a thermoplastic polymer. The oxidizer may be, withoutlimitation, bimodal ammonium perchlorate (AP), ammonium nitrate,ammonium dinitramide, and the like.

An example formulation for a cast of a 4% nMx fuel grain is given inTable 9.

TABLE 9 A non-limiting example or a cast solid fuel grain having 4% nMxas a burn rate enhancer for an SRM. Ingredient % Addition AP - powderedoxidizer 78.0% LV HTPB - rubber binder 9.0% IDP - plasticizer 1.0% Al 32um - fuel 4.0% 143L - liquid curative 3.0% nMx - nanocomposite 4.0%additive Castor Oil - density and 1.0% strength improvement

To achieve a solid fuel grain for a hybrid engine, where reactants arein different physical states, usually a solid fuel is made to meet agaseous oxidizer. At least two burning ingredients are cast into asingle mold, a non-limiting example being nMx being cast with a massfrom about 0.05% to about 50%, a binding agent being cast with a massfrom about 1% to about 50%. A gaseous oxidizer flows through an intakeopening into and over the nMx containing solid fuel and releases througha nozzle as exhaust. The nMx solid fuel is ignited by an igniterpositioned proximal to where the oxidizing gas first contacts the fuelnear the intake. In one embodiment of a solid fuel chamber for a hybridengine, the solid nMx fuel bodies generally have a center elongated flowchannel through which the oxidizer flows after ignition for ablating thefuel on the side walls of said channel.

Ingredients for a Cast or 3D Printed nMx Fuel Grain

What follows are the ingredients used to press, cast, or 3D print nMxinto a solid fuel gain to use in a SRM or HRM system.

The solid fuel grain of the present invention is associated with atleast one variation of nMx as outlined above. nMx is a singular materialthat is air stable and is a nanocomposite of Li₃AlH₆ nanoparticles,elemental Al nanoparticles, an amount of Ti metal, and a nanoscaleorganic layer. nMx protects and preserves the high energy densities ofthe core metals isolated from a controlled bottom up reaction and makesthe nanoparticles safe to handle in air. nMx is lightly ground into afine powder and sieved to size for enhanced surface area and uniformitywithin the solid propellant. nMx may be pressed, cast, or 3D printedwithin a solid fuel grain with a mass from about 0.05% to about 50%along with a thermoset polymer or a thermoplastic polymer being pressed,cast, or 3D printed with a mass from about 1% to about 50%.

The binder of the present invention gives structural integrity to thefuel grain and may either be a thermosetting or thermoplastic polymer.Thermoset polymers in their liquid polymer forms must be cured bycross-linking molecules to harden the material into shapes. Once curedthe thermoset polymer cannot be remelted or reprocessed for any otheruses. Because of their sensitivity to high temperatures, thermosetpolymers are not well suited for 3D printing applications. Thermosetpolymers do not melt when heated by instead char and ablate. Thermosetpolymers must be used from their liquid forms, degassed, and then castand cured. As such, traditional casting methods known in the art arebest for shaping the final fuel grain having at least one nMx composite,a thermoset polymer as a binder, and optionally an oxidizer, curingagents, and other additives.

The thermoset polymer acts as a binder and is typically an elastomerichydrocarbon polymer formed by the chain extension and cross-linking offunctionally terminated liquid polybutadiene polymers. These binders mayinclude without limitation: Low Viscosity HTPB (hydroxyl-terminatedpolybutadiene/LV HTPB), polyurethane or polybutadienes ((C₄H₆)_(n)),e.g., polybutadiene-acrylic acid (PBAA) or polybutadiene-acrylic acidterpolymer (such as polybutadiene-acrylic acid acrylonitrile (PBAN)),which can be crosslinked with isophorone diisocyanate; or carboxylterminated polybutadiene (CTPB). Elastomeric polyesters and polyethersmay also be included as binders for the present invention. The bindermay be polymerized during rocket motor manufacture and is typicallyconsumed as part of the fuel during burning, which also contributes tooverall specific impulse of the system.

The thermoplastic polymer of the present invention is suitable as a basepolymer for 3D printing applications. Instead of a binder, indicatingthe use of cross-linking agents, the thermoplastic acts as a matrix forthe nMx composite and other additives. A thermoplastic polymer becomessoft and pliable when heated. It does not cure. There is no need forcross-linking or curing agents. Once the thermoplastic hardens into theshape as supplied by the 3D print instructions, the thermoplastic coolsand hardens into that shape.

Thermoplastic polymers of the present invention are compatible with anycommercial 3D printer and may include without limitation: polypropylene,PP Homopolymer (HPPP), PP Copolymer (CPPP), Polylactic Acid (PLA),acrylonitrile-butadiene-styrene (ABS), High Impact Polystyrene (HIPS),Thermoplastic Elastomer (TPE), Ethylene Vinyl Acetate (EVA), PolyAmide(PA), PE Low Density (LDPE/LLDPE), PE High Density (HDPE), ThermoplasticElastomer, Polyphenylene Sulphide, thermoplastic polyurethane orpolybutadienes ((C₄H₆)_(n)), e.g., polybutadiene-acrylic acid (PBAA) orpolybutadiene-acrylic acid terpolymer (such as polybutadiene-acrylicacid acrylonitrile (PBAN)), which can be crosslinked with isophoronediisocyanate, styrene block-copolymers, thermoplastic siliconeelastomer, aliphatic or semi-aromatic polyamides, thermoplasticvulcanisate, polyvinyl alcohol, polycarbonate, polylactic acid,polymethylmethacrylate, polyethylene, polystyrene, nylon, polycarbonate,polyvinyl chloride, or Teflon, or any combinations thereof.Acrylonitrile-Butadiene-Styrene polymer (ABS), as provided by (FilabotInc), has a print temperature of about 200° C.-230° C. and an extrusiontemperature of 175° C.-190° C. The specific gravity is 1.04, and the ABSpellets are typically molding grade.

The solid fuel grain of the present invention is associated with apowdered oxidizer, where the oxidizer may include without limitation,ammonium perchlorate (NH₄ClO₃) powder, metal perchlorates, ammoniumnitrate and ammonium dinitramide (NH₄N(NO₂)₂) or for an HRM theoxidizers are in their gaseous form.

The plasticizer of the present invention reduces viscosity of the fuelgrain. Plasticizers may include without limitation dioctyl sebacate,dioctyl adipate (“DOA”), isodecyl perlargonate (IDP), dioctyl phthalate(“DOP”), or mixtures thereof.

The fuel of the present invention may include without limitation powdersof the following metals or alloys: micron aluminum (Al 32 μm or 44 μm),beryllium, zirconium, titanium, boron, magnesium, or alloys andcombinations thereof. The fuels are preferably pure metals, where thepowders have a maximum dimension of 500 μm or less. However, nanometerpowders with dimensions from 25 nm up to 500 nm may also be used. Themetal fuel can have various shapes, including but not limited tospherical, flake, irregular, cylindrical, or any combinations thereof.

The present invention includes a curing agent to cure or crosslink thethermoset polymer. The curing agent may include without limitationModified diisocyanate (143 L), polyurethane hexamethylene diisocyanate(“HMDI”), isophorone diisocyanate (“IPDI”), toluene diisocyanate(“TDI”), trimethylxylene diisocyanate (“TMDI”), dimeryl diisocyanate(“DDI”), diphenylmethane diisocyanate (“MDI”), naphthalene diisocyanate(“NDI”), dianisidine diisocyanate (“DADI”), phenylene diisocyanate(“PDI”), xylene diisocyanate (“MXDI”), ethylenediisocyanate (“HDI”),other diisocyanates, triisocyanates, polyfunctional isocyanates, or anycombinations thereof.

The fuel grain's bonding agent includes a viscous material that adheresthe propellant grain and improves the density thereof and may includewithout limitation: coconut oil, palm oil, cottonseed oil, vegetableoil, soybean oil, olive oil, peanut oil, corn oil, sunflower oil,safflower oil, jojoba oil, canola oil, shea butter, cocoa butter, milkfat, amaranth oil, apricot oil, argan oil, avocado oil, babassu oil, benoil, algaroba oil, coriander seed oil, false flax oil, grape seed oil,hemp oil, kapok seed oil, meadowfoam seed oil, okra seed oil, perillaseed oil, tepanol, poppyseed oil, prune kernel oil, pumpkin seed oil,quinoa oil ramtil oil, rice bran oil, camellia oil, thistle oil, wheatgerm oil or any combinations thereof.

The above examples for making either a solid or hybrid fuel grain havingnMx as an ingredient lies in the nanocomposite's unique burn ratecharacteristics. The burn rate of a material may be thought of as thedistance traveled per second by a flame perpendicularly exposed to asurface of a material. The burn rate for a material is dependent uponthe pressure of the surrounding gas phase within a container. For asolid rocket motor to achieve the greatest thrust possible, it must burna large amount of fuel/oxidizer in a short amount of time, whileexpelling combustion gases out of a nozzle, where our data seems toindicate that nMx nanocomposite materials are well suited for thisevent.

3D Printing nMx Fuel Grains

It is an embodiment of the present invention where at least one nMxcomposite is embedded in a bulk thermoplastic matrix, being a basematerial or feed stock for 3D printing solid fuel grains. The basematerial is compatible for 3D Printing, extrusion moulding, andinjection moulding, where any of these processes shape, layer, or printthe base material into a final construct that is endowed with nMx'sunique burn characteristics. In addition to solid fuel grains, the basematerial may be used to print via a 3D printer an explosive, a photonic,a plasmonic, and the like.

3D Printing technology is used with applications in architecture,industrial design, automotive, aerospace, military, civil engineering,medical industries, biotech, and many other fields. Selective LaserSintering (SLS®), Fused Deposition Modeling (FDM)™, the various forms ofStereolithography, and Continuous Liquid Interface Production are allforms of 3D Printing that include a computer associated with a 3Dprinter scanning a file format exported from a 3D modeling program thatcontains the spatial points for creating the fuel grain.

With the present invention, an nMx composite may either be introducedinto a thermoplastic polymer either in a solvent based reaction orduring the hot melt delivery of the thermoplastic to a printing platformduring the layering process as executed by a 3D printer. Either processcreates a base material that has energetic properties suitable as asolid fuel grain for combustion applications.

It is an embodiment of the present invention where the nMx base materialis compatible with a 3D printer capable of fuse deposition modeling(FDM) to make solid fuel grains for an solid rocket motor (SRM) orhybrid rocket motor (HRM) system. Although the disclosed method usesFDM, the base material should be compatible with 3D printers that employSelective Laser Sintering (SLS®), Stereolithography, Continuous LiquidInterface Production, powder bed printing, and/or Inkjet Head printing.The solid fuel grain may be layered via other methods known within thearts, including but not limited to, extrusion deposition, binding ofgranular materials, lamination, or photo polymerixation. The polymermaterial can be virtually any thermoplastic elastomer with sufficientfatigue resistance.

These materials may include without limitation: a powdered oxidizer, athermoplastic polymer, a plasticizer, a metal fuel, a curing agent, acure catalyst, ballistic catalysts, burn rate catalysts or modifiers, oran oil or wax. These optional ingredients may be added with nMx in a drypowder form before combining the nanocomposite with the thermoplasticpolymer in the hot melt process at a 3D printer, or, alternatively, thethermoplastic polymer may be softened in a separate process, by methodsknown within the art, and the optional ingredients added to the samebefore being heated and layered by a 3D printer.

Burning and Test Firing of nMx Fuel Grain

nMx may be incorporated into a hybrid or solid fuel grain forperformance increase delivered by the nanoparticles. We can mix nMx₂₀,or any iteration of thereof, into solid rocket formulations for testingpurposes and eventual applications in rocket and missile motors. Fuelgrains were made according to any of the methods listed above for anSRM. However, these methods can also be made for HRMs less the oxidizerin the cast. Each of the four testing grains contained 8% of acombination of 4%-micron aluminum powder and 4% nMx₂₀. The rest of thesolid fuel grain contained the following constituents: 78% bimodalammonium perchlorate [oxidizer]; 9% low viscosity HTPB[binder]; 1% IDP[plasticizer]; 3% 143 L [curative]; 1% castor oil [bonding agent].

A firing test for an nMx fuel grain in an SRM and the data collectionmethod are as follows: a motor diameter of 38 mm, a solid fuel grainbeing multiple-segment, where each segment is a hollow cylindrical grainthat is case bonded. The initial burning surface areas are at the portcore and segment ends, and the cylinder cast is inhibited to burningfrom outside to inside. The port is drilled directly though the centerof the grain at 7/16″. The nozzle size is about 0.291″ at throat andabout 0.688″ at the exit. The fuel grain has dimensions of 38 mmdiameter (1.5″)×3.6″ length grains. A 100 kg S-type load cell, aspurchased from RobotShop, is used to measure the SRM thrust. A 9milelake 1600 psi stainless steel pressure sensor is used to collectpressure data. The fuel grain is ignited within the SRM casing via anelectronic match igniter (Wildman Rocketry) as dipped in Pyromag pyrogenby Firefox Enterprises, LLC and set off with a 12V battery. The chamberpressure is ambient until ignition and formation of hot gasses. Due tothe complexity of nMx's burn profile in relation to the primary fuel forthe propellant, burn rate is to be determined.

Our SRM test gives Isp data (seconds) as reported below in Table 10,where thrust is in Newtons and derived from the force/mass fluxrelationship as mentioned above. Four firings, SRMs a-d are recorded atroom temperature under ambient pressure before firing. The HTPBpre-polymer is a viscous liquid until the curative is added. Notemperature changes were applied through the entire process.

TABLE 10 Isp (s) calculations for nMx₁₂ and nMx₂₀ SRM Formulation FuelsIsp (s) a Al [8%] 188 b Al [4%] + nMx₁₂ [4%] 186 c Al [4%] + nMx₂₀ [4%]192 d Al [4%] + nMx₂₀ [4%] 190

The nMx enhanced fuel grains show a greater contribution to performancerelative to 8% Al micron powders. However, nMx₁₂ gives a slightly lowerIsp number due to the possibility of having less O atom in the nanoscaleorganic layer. Energy densities are maintained, allowing nMx₂₀ toincrease specific impulse by ˜2-4 seconds when compared to the baselinefirings of 8% micron aluminum. If the estimated delivered energy densityof aluminum is taken as 20 kJ/g, and the theoretical energy density ofnMx₂₀ is −30 kJ/g, an energetic increase of 50% in 4% of the formulationwould lead to a rough performance increase of 2%, which data areindicated. To utilize more nMx's energy density, especially nMx₁₂,larger motors should be used to achieve complete combustion and fulleffect.

Since some delamination was seen with higher percentages of nMx (failureat 8%), more binder may be used to provide better structural integrity.Alternate bonding agents and binders are also being explored to allowhigher incorporation of nMx without strong chemical incompatibility.

Another important testing avenue is to determine the performanceimprovement of nMx cores with reduced organic cap. With reduced cap, thekinetics and combustion ability of the material will be improved, andthe density will improve slightly. Also, new handling procedures underinert atmosphere make stronger the viability of processing the reducedorganic material into usable, high energy fuel grains.

Approximately 3 grams of commercial aluminum powder and nMx powder isweighed and placed on a flat metal surface. Each powder is spread in aneven line measuring 150 mm, measured with calipers. A video recording isstarted, and a propane torch is used to light one end of each line ofpowder. After combustion is complete, the video is digitally analyzed todetermine linear burn rate in length per time.

Table 11 presents linear burn rates taken at atmospheric pressure forpure nMx powders and Novacentrix 80 nm commercial grade aluminum powderin mm/sec. This data indicates that nMx displays an extremely highlinear burn rate as compared to the state of the art, being Novacentrix80 nm aluminum powder. Note that, nMx₁₂ HC and nMx₂₀ HC [High Core]designate a balance between the nanoscale organic layer and the coremetal nanoparticles of ⅓ and ⅔ by weight respectively. Reducing aportion of the nanoscale organic layer allows the combustion reaction toaccess the cores quicker for faster burn rates. This ambient burn showsthat the nMx HC powders display significantly better burn rates againstthe standard aluminum powders. It is an embodiment of the presentinvention to tune the fraction of the nanoscale organic layer about thesurfaces of both core metal nanoparticles to be about 25% to about 75%by weight to modify the burn rate characteristics of an nMx composite.

TABLE 11 Linear burn rates in atmospheric pressure for pure nMx powdersand commercial comparison powders. Burning Material Burn Rate (mm/sec)Novacentrix 80 nm 5 Aluminum Powder nMx₁₂ 4 nMx₁₆ 6 nMx₂₀ 110 nMx₁₂ HC14 nMx₂₀ HC 100

What follows are two non-limiting examples of introducing the nMxcomposite into a thermoplastic polymer. One example is via a solventbased reaction that influence the state of the thermoplastic polymer andthe other is via heat as supplied by elements of a 3D printing machineusing the FDM technique. However, these examples are not a limitation ofthe scope of the invention but are present only as examples.

Solvent Reaction for an nMx (20% m/m) Base Material for 3D Printing

nMx in an ABS polymer has been produced. The formulation consists of 20%m/m nMx in 80% m/m ABS. A non-limiting example of the reaction is asfollows. Once the nMx particles are synthesized and acquired as above, aSchlenk line connected to a vacuum and an Argon gas line is used toproduce an Acrylonitrile-Butadiene-Styrene (ABS) polymer embedded withnMx powder. However, the use of this polymer is non-limiting and may bereplaced by any suitable polymer to form an nMx based matrices. The nMxpowder is a defined as a nanocomposite being Li₃AlH₆ nanoparticles,elemental Al nanoparticles, an amount of Ti metal, and a nanoscaleorganic layer.

A vacuum trap is connected to the Schlenk line to trap any solventremoved from the reaction mixture dispersion. The Schlenk line isconnected to two bubblers on either side to indicate Argon gas flow inand out of the Schlenk line. A needle valve is used to control the flowof Argon gas within the apparatus, and the Ar gas is provided by acompressed tank installed with a regulator. Vacuum hoses connected toall the ports on the Schlenk line and the connections within the generalsetup. To contain any dispersions and reaction mixtures, air-free glassflasks are used. These flasks contain a stopcock valve to expose itscontents to either vacuum or Argon gas. Luer lock syringes are used totransfer and mix any dispersions.

4 g of ABS is dissolved in ˜30 mL of distilled THF within an air-freeflask. A magnetic stirrer is included, and the stirring is used toagitate and dissolve the ABS. Eventually, the ABS is fully dissolved in˜30 minutes. In another air-free flask, 1 g of the organic polymercapped nMx powder is dissolved in 60 mL of distilled THF for the 20% nMxformulation. The organic polymer capped nMx powder is not verydispersible, but agitation is able to suspend the powder. A stirrer isincluded into the flask to stir and agitate the suspension.

With a Luer lock syringe, the ABS solution is drawn and injected intothe organic polymer capped nMx dispersion while stirring. The combineddispersion of ABS and organic polymer capped nMx powder is left to stirfor ˜30 minutes. Then, it was vacuumed at room temperature to remove theTHF solvent. Stirring is still present while vacuuming to agitate andimprove the efficiency of the removal. After the solvent is removed, aplastic sheet or film of ABS with embedded organic polymer capped nMx isproduced. It is a dark black or gray sheet that sticks to the glass. Itcan be removed with a spatula. The nMx powder is uniformly distributedin the thermoplastic, where ratios for the resulting composition ofmatter [Li₃AlH₆:Al:Ti:NSOL]:ABS exist from about 3:1 to about 1:100.

The resulting mixture of the nanocomposite and the ABS thermoplasticpolymer is a base material that is suitable for 3D printing a fuel grainfor either an SRM or HRM. The base material may be ground into powderparticles that may be sintered or melted to form via Selective LaserSintering (SLS®) until the solid fuel grain is constructed.Alternatively, the base material may be layered when melted beads of thethermoplastic polymer meet nMx powder in a dual heated nozzleconfiguration for Fused Deposition Modeling™. Alternatively, the basematerial maybe formed as a bead containing nMx, the thermoplasticpolymer, and other additives and then used as base polymer or feed stockfor a 3D printer for printing a fuel grain construct.

It is an embodiment of the present invention where the base materialsshape and method of combining the nMx nanocomposite and thethermoplastic polymer may be altered to ensure compatibility with any ofstereolithography, laminated object manufacturing, ink jet headprinting, or other photopolymer based 3D printers without departing fromthe spirit of the invention and any changes that are contemplated by oneof ordinary skill in the art to make the base material compatible withthese 3D printing processes are captured by this specification.

Fuse Deposition Modeling of an nMx Fuel Grain

It is an embodiment of the present invention where the ingredients for abase material used to 3D print a solid fuel grain for either a SRM orHRM may be combined at or near the nozzle of a 3D printer during the hotmelt process before the base material is layered by the same. All formsof 3D Printers include a computer having a 3D modeling program thatcontains the spatial points for creating a construct. A user exportsdigital instructions for a fuel grain shape from the 3D modeling programto a computer located at the 3D printer. The digital instructions arespatial points that create a 3D template for layering the fuel grain inthe real world. Layering is done from the bottom surface up. 3D printerfile formats include, but are not limited to, .stl (standard triangularlanguage), .obj, PLY, or the like.

The computer of the present invention includes one or more deviceshaving one or more processors capable of communicating with the othercomponents of the system. The computer typically receives many inputsand outputs for communicating information externally to a 3D printingsystem. Non-limiting examples of inputs and outputs may include: akeyboard, a mouse, a trackball, a joystick, a touchpad, and/or amicrophone, a CRT monitor, and/or an LCD display panel.

Communication may either be a wireless frequency signal or a directwired communication signal that sends instructions to a 3D printer forprinting an nMx fuel grain. The processor can execute computer programs,e.g. 3D modeling programs, with instructions for printing an nMx fuelgrain stored in a computer-readable medium or memory such as arandom-access memory (“RAM”), read only memory (“ROM”), and/or aremovable storage device. The computer should have a basic operatingsystem, such as MS Windows, Linux, Mac OS, or the like. The fuel graininstructions may comprise code from any computer-programming language,including, C, C++, C#, Visual Basic, Java, Python, Perl, and JavaScript.

Suitable processors may comprise a microprocessor, an ASIC, and statemachine. Example processors can be those provided by Intel Corporation,AMD Corporation, and Motorola Corporation. Such processors comprise, ormay be in communication with media, for example computer-readable media,which stores instructions that, when executed by the processor, causethe processor to perform the elements described herein.

Within a 3D modeling program, points and line segments in a Cartesianplane, e.g. an [x, y, z,] Cartesian system, are used as predeterminedspatial instructions or can be drawn free hand to create virtually solidmodels of the solid fuel grain having nMx. The construct will haveweight, density, and a center of gravity in either case. The fuel gainin its final form will be tangible and can be readily used in combustionprocess for a SRM or hybrid rocket motor HRM systems.

The digital instructions for making a fuel grain can be stored in memoryor the processor. The computer program for creating the fuel grain areof the type typically used for rapid prototyping or manufacturinginstructions, including but not limited to: 3DMLW (3D Markup Languagefor Web), Dassault Systemes graphic representation, Virtual ArchitectureCAD, Ashlar-Vellum Argon-3D Modeling, ArtCAM model, BRL-CAD Geometry,Solidedge Assembly, Pro/ENGINEER Assembly, Data Design System DDS-CAD,CopyCAD Curves, CopyCAD Model, CopyCAD Session, CadStd, CATIA V5 Drawingdocument, CATIA V5 Part document, CATIA V5 Assembly document, CATIA V5Manufacturing document, AutoCAD and Open Design Alliance applications,Solidedge Draft, MicroStation design file, Delcam Geometry, DelcamMachining Triangles, ASCII Drawing Interchange file format—AutoCAD,VariCAD drawing file, Wilcom—Wilcom ES Designer Embroidery, Agtekformat, EXCELLON, FeatureCAM, FormZ, BRL-CAD, GERBER, T-FLEX CAD,GRAITEC, Auto CAD, Solidworks, Autodesk Inventor, Fusion 3D, Rhino 3D,Alias, Pro-Engineer Sketchup, and the like.

Any generic program should be capable of sweeping, extruding, revolving,lofting, slicing, sculpting of a surface, or converting connected pointsforming 2D parametric contours and straight lines into any imaginable 3Dshape. Fused Deposition Modeling (FDM)™ includes a computer associatedwith a 3D printer that slices a file format exported from a 3D modelingprogram. The sliced program creates a tool path for heated nozzles. Thedata is then sent to another part of the printer, which thenmanufactures the solid fuel grain layer by layer on a build platform.

A dual heated nozzle configuration may extrude materials and preciselylay them down in successive layers, where the nozzles move as an x-yplotter, and the platform moves, or drops, with a z motion according tothe tool path of the solid fuel grain. A suitable system is availablefrom Stratasys, Incorporated of Minneapolis, Minn. FDM printers mayinclude without limitation The Stratasys Fortus 900, The StratasysPolyjet machines, The Stratasys Connex machines, The Ultimaker machines,The Makerbots Rep 2, and 5th Generation machines. One nozzle isconnected to a reservoir containing the nMx powder and another nozzle isconnected to the thermoplastic polymer, which may either be a bead orwound about a spool the feeds the nozzle.

The thermoplastic polymer and the nMx powder are used to create eachcross section of the solid fuel grain. As the heated nozzle softens thethermoplastic, nMx powder sprayed from one of the dual nozzles into aheating zone to disperse the nanocomposite within the softenedthermoplastic polymer before the nozzle reacts to the layeringinstructions from the 3D software program. The thermoplastic polymer andthe nMx nanocomposite are layered at the same time and the extruded basematerial can harden. The process is repeated based on the 3Dinstructions for the solid fuel grain now located at 3D printer untilthe 3D solid fuel grain is complete.

The semi-fluid formulation may be cast into a motor casing. Acylindrical type casing can be made prior to casting. It is anembodiment of the present invention where the fuel grain may be cast,molded, extruded, or in some instances machined into a cylindricallyshape having a center port that is star shaped, a circular shaped,Maltese cross shaped, clover shaped, helix shaped, double anchor, rod intube, and the like, so long as there is an outer cylindrical body havingtwo distal ends and a hollow inner cavity, or port, with a shape that isdesigned to maximize the burn rate characteristics of an SRM or HRMsolid fuel grain.

The solid fuel grains as described herein, being a thermoset polymer ora thermoplastic polymer matrix with nMx, may be used with SRMs or HRMsknown within the art. A typical SRM will at least include a motor withan igniter, a head closure cap, a cylindrical case/combustion chamber,and a nozzle. The igniter, having a pyrotechnic that releases andtransfers heat about the inner surfaces of the fuel grain's port, startsthe thrusting event by igniting these surfaces to combustion and flamesto form. The solid propellant of the present invention may be packedinto a combustion chamber under pressure or, alternatively, created as acylindrical elongated construct having two distal ends with alongitudinally extending bore, a port, therein. For an HRM, the fuelgrain is less an oxidizer as an additive and the port is made to meetvia an injector or valve a gaseous flow of an oxidizing material held ina separate container near the combustion chamber.

The foregoing words describe embodiments for a nanocomposite having twodistinct nanoparticles that render unique burning characterizes. Abottom up synthesis creates nanoparticles that are carefully sized andpassivated at the controlled first reaction step of LiAlH₄decomposition. The nanocomposite is air stable being Li₃AlH₆nanoparticles, elemental Al nanoparticles, an amount of Ti metal, and ananoscale organic layer, which protects and preserves the high energydensities of the nanoparticles isolated from the precisely controlledreaction. All compositions of matter, methods for making the same,and/or uses of the present invention disclosed and claimed herein can bemade and executed without undue experimentation. However, these wordsare not a limitation on the scope of the present invention but arewritten to detail certain embodiments thereof. Changes made by one ofordinary skill in the art to our invention does not alter and take awayfrom the scope and spirit of our invention and are meant to be capturedherein. Thus, the scope of the present invention may be defined by thefollowing claims.

REFERENCES

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We claim:
 1. A nanocomposite for combustion applications comprising: a.a homogenous mixture of two distinct core metals including a firstnanoparticle that is a metal hydride, a second nanoparticle that is anelemental post-transitional metal; and b. wherein the surfaces of bothnanoparticles are: i. associated with an amount of titanium metal; andii. are air stabilized by a nanoscale organic layer being a fatty acid,a fatty alcohol, an alkadiene, or any mixture or combination thereof. 2.The nanocomposite of claim 1, wherein the first nanoparticle is Li₃AlH₆and the second nanoparticle is elemental Aluminum metal, wherein bothare associated with an amount of titanium metal and are passivated andair stabilized by a nanoscale organic layer.
 3. The nanocomposite ofclaim 2, wherein the nanoscale organic layer is a fatty acid, a fattyalcohol, an alkadiene, or any mixture or combination thereof, whereinthe nanoscale organic layer passivates and air stabilizes the surfacesof both the Li₃AlH₆ nanoparticle and the elemental Al nanoparticle andincludes: 1,7-octadiene, 1,9-decadiene, myrcene, or 1,13-tetradecadiene,1,3-butadiene, isoprene, 2-methyl-1,3-pentadiene,2,3-dimethyl-1,3-butadiene, 1,3-pentadiene,2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-pentadiene,1,3-hexadiene, 2-methyl-1,3-hexadiene, 1,3-heptadiene,3-methyl-1,3-heptadiene, 1,3-octadiene, 3-butyl-1,3-octadiene,3,4-dimethyl-1,3-hexadiene, 3-n-propyl-1,3-pentadiene,4,5-diethyl-1,3-octadiene, 2,4-diethyl-1,3-butadiene,2,3-di-n-propyl-1,3-butadiene, and 2-methyl-3-isopropyl-1,3-butadiene,fatty alcohols being tert-butyl alcohol, tert-amyl alcohol,3-methyl-3-pentanol, ethchlorvynol, 1-octanol (capryl alcohol),pelargonic alcohol (1-nonanol), 1-decanol (decyl alcohol, capricalcohol), undecyl alcohol (1-undecanol, undecanol, hendecanol), laurylalcohol (dodecanol, 1-dodecanol), tridecyl alcohol (1-tridecanol,tridecanol, isotridecanol), myristyl alcohol (1-tetradecanol),pentadecyl alcohol (1-pentadecanol, pentadecanol), cetyl alcohol(1-hexadecanol), palmitoleyl alcohol (cis-9-hexadecen-1-ol), heptadecylalcohol (1-n-heptadecanol, heptadecanol), stearyl alcohol(1-octadecanol), nonadecyl alcohol (1-nonadecanol), arachidyl alcohol(1-eicosanol), heneicosyl alcohol (1-heneicosanol), behenyl alcohol(1-docosanol), erucyl alcohol (cis-13-docosen-1-ol), lignoceryl alcohol(1-tetracosanol), ceryl alcohol (1-hexacosanol), 1-heptacosanol,montanyl alcohol, cluytyl alcohol, or 1-octacosanol, 1-nonacosanol,myricyl alcohol, melissyl alcohol, or 1-triacontanol, 1-dotriacontanol(lacceryl alcohol), geddyl alcohol (1-tetratriacontanol), cetearylalcohol, carboxylic (fatty) acids being butyric acid [CH₃(CH₂)₂COOH],valeric acid [CH₃(CH₂)₃COOH], caproic acid [CH₃(CH₂)₄COOH], enanthicacid [CH₃(CH₂)₅COOH], caprylic acid [CH₃(CH₂)₆COOH], pelargonic acid[CH₃(CH₂)₇COOH], capric acid [CH₃(CH₂)₈COOH], undecylic acid[CH₃(CH₂)₉COOH], lauric acid [CH₃(CH₂)₁₀COOH], tridecylic acid[CH₃(CH₂)₁₁COOH], myristic acid [CH₃(CH₂)₁₂COOH], pentadecylic acid[CH₃(CH₂)₁₃COOH], palmitic acid [CH₃(CH₂)₁₄COOH], margaric acid[CH₃(CH₂)₁₅COOH], stearic acid [CH₃(CH₂)₁₆COOH], nonadecylic acid[CH₃(CH₂)₁₇COOH], arachidic acid [CH₃(CH₂)₁₈COOH], or any combinationsthereof.
 4. The nanocomposite of claim 3, wherein the nanocomposite hasa measured energy density from −38 kJ/g to −35 kJ/g.
 5. Thenanocomposite of claim 3, wherein the nanoscale organic layer alsoincludes glycols, having various molecular weights, being PEG, PEO,tetraethylene glycol, triethylene glycol, or any combination thereof inmixture with a fatty acid, a fatty alcohol, or an alkadiene.
 6. Thenanocomposite of claim 4, wherein the nanoscale organic layer is acombination of octadecanol and tetraethylene glycol in a respectiveratio mixture of 23% to 77% or 70% to 30% and has an energy density of−29 kJ/g.
 7. The nanocomposite of claim 4, wherein the nanoscale organiclayer is a combination of steric acid and tetraethylene glycol in arespective ratio mixture of 23% to 77% or 70% to 30% and has an energydensity of −29 kJ/g.
 8. The nanocomposite of claim 1, wherein the amountof titanium metal associated with the Li₃AlH₆ nanoparticles and theelemental Al nanoparticles is from 0.05% to 1.0% of the total weight ofthe nanocomposite.
 9. The nanocomposite of claim 2, wherein the Li₃AlH₆nanoparticles have a diameter from 15 nm to 100 nm and the elemental Alnanoparticles have a diameter from 7 nm to 100 nm.
 10. The nanocompositeof claim 1, wherein the amount of titanium metal associated with thesurfaces of both the Li₃AlH₆ nanoparticles and the elemental Alnanoparticles originates from a titanium alkoxide, a titanium(IV)compound, titanium(IV) tetraalkoxylate, titanium(IV) isopropoxide(Ti(O^(i)Pr₄, 97%), or a titanium(IV) tetraaryloxylate.
 11. Thenanocomposite of claim 2, wherein the nanoscale organic layer about thesurfaces of both core metal nanoparticles are fractionally tuned from25% to 75% by weight to modify the burn rate characteristics of thenanocomposite.
 12. The nanocomposite of claim 1, wherein thenanocomposite exhibits a combustion event for the Li₃AlH₆ nanoparticlesbetween 180° C. and 210° C., a combustion event for the nanoscaleorganic layer between 275° C. and 325° C., and a combustion event forthe elemental Al nanoparticles between 575° C. and 610° C.
 13. Thenanocomposite of claim 1, wherein the nanocomposite is characterized byPXRD peaks for both nanoparticles and the Raman fundamental stretchingfrequencies of nanoscale organic layer as follows: Li₃AlH₆ nanoparticlesgiving a PXRD diffractogram having double peaks for 2Θ at 21.9°, at22.5°, and at 31.7°; elemental Al nanoparticles giving PXRD peaks at 2Θat 38.4° [highest peak], 44.7°, at 65.1°, at 78.2°, and 82.4°; and thenanoscale organic layer giving Raman data for C—O stretching frequenciesfrom 1092 cm⁻¹ to 1294 cm⁻¹, C═O stretching frequencies of 1645 cm⁻¹,and C—H stretching frequencies from 2839 cm⁻¹ to 3024 cm⁻¹.
 14. Thenanocomposite of claim 1, wherein the nanoscale organic layer is amonomer that can undergo polymerization, cross-linking, orcopolymerization to form a matrix about both distinct nanoparticles. 15.The nanocomposite of claim 2, wherein the nanoscale organic layer forboth Li₃AlH₆ nanoparticles and elemental Al nanoparticles imparts airstability to the nanocomposite for safe handling in ambient conditionsand wherein the nanoscale layer contains an oxygen atom mass from 5% to34%.